Respiratory System Lab
Learning Objectives
- Describe the changes in the type of epithelium throughout the respiratory system
- Explain how the structure of different segments of the respiratory airways reflect the functional roles that these airways play in air movement and gas exchange
- Distinguish the trachea, bronchi, terminal bronchioles, bronchioles, alveolar ducts, alveolar sacs, and alveoli based on key structural features
- Identify the different types of pneumocytes and their functions
- Recognize key pathological conditions associated with the respiratory tract
Pre-Lab Reading
Introduction
The respiratory system consists of two divisions with distinct structural elements that reflect their unique functions. These include:
- The conducting airways, which serve to conduct, clean, warm, and moisten the air. This portion is composed of the nose, pharynx, larynx, trachea, bronchi, and bronchioles.
- The respiratory airways, which facilitate gas exchange. These are located entirely within the lung and are represented by respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.
Conducting Airways
The epithelium lining the respiratory tract from the nasal fossa through the bronchi is called the respiratory mucosa and is characterized by a pseudostratified ciliated epithelium with abundant non-ciliated cells known as goblet cells. In the lamina propria there are mixed seromucous (protein- and mucous-secreting) glands, lymphatic tissue, and broad veins.
The conducting airways are divided into two main sections:
The conducting airways are divided into two main sections:
- Extrapulmonary air conduits are located outside of the lungs and begin with the nose, pharynx and larynx. The trachea is continuous with the larynx above and the two primary bronchi below. It is the supporting framework for 16-20 C-shaped hyaline cartilages. These cartilage "bracelets" are open on the posterior wall of the trachea adjacent to the esophagus. A bundle of smooth muscle fibers bridges the gap between the two ends of the cartilage.
- Intrapulmonary air conduits extend from the intralobar bronchi to the terminal bronchioles. When the bronchi enter the lung, the C-shaped cartilages that characterize the trachea and primary bronchi are replaced by irregular plates or cartilage that completely surround the cylindrical muscular airway tube. Cartilage disappears in the terminal bronchioles, which have narrowed to a diameter of 1 millimeter. The terminal bronchioles initially have a ciliated columnar epithelium that soon transitions to a low cuboidal epithelium. Mucous and seromucous glands and diffuse lymphatic tissue are associated with smaller bronchi but are not found distal to the region where there is a loss of cartilage plates.
Respiratory Airways
The respiratory airways extend from the respiratory bronchioles to the alveoli.
- The respiratory bronchioles have a diameter of 0.5 millimeters and feature a few alveoli scattered along their walls. The epithelium here remains low cuboidal. Each respiratory bronchiole branches into between 2 and 11 alveolar ducts that still contain smooth muscle fibers in their walls. Along these walls, the alveolar ducts give rise to single alveoli and to numerous alveolar sacs, which are associated with 2 to 4 alveoli. The space at the entrance from the alveolar duct to an alveolar sac is referred to as the atrium.
- Alveoli can be studied most easily in preparations of expanded lung, especially in those areas in which erythrocytes have been retained in the capillaries. Alveoli have a distinct cup shape separated by loop- or crescent-shaped walls known as interalveolar septa. The interalveolar septa contain myriad capillaries.
The interface between the capillary lumen and the alveolar epithelium is known as the air-blood barrier. The barrier consists of the endothelium of the capillary, the epithelium of the alveolus, and their shared basement membrane.
The surface epithelium of the alveoli contains two developmentally related but functionally distinct cells, known as pneumocytes. Type I pneumocytes are attenuated vesicle-studded cells that line the alveolar walls near the capillaries. Only their flattened nuclei can be recognized with certainty by light microscopy. Type II pneumocytes are cuboidal and occur singly or in small clusters between type I cells. They contain 0.2 to 1 micron wide multilamellar bodies that contain a high content of phospholipid that is the precursor to pulmonary surfactant, which interferes with the surface tension in the alveoli that would otherwise cause them to collapse. Club (Clara) cells are also thought to participate in the synthesis of surfactant. Type II cells serve as precursors to type I cells.
Where there are no capillaries, the alveolar septum contains fibroblasts, collagen, elastic fibers, smooth muscle cells, and macrophages known as dust cells. Also notable are alveolar pores, which equalize air pressure between the alveoli.
The surface epithelium of the alveoli contains two developmentally related but functionally distinct cells, known as pneumocytes. Type I pneumocytes are attenuated vesicle-studded cells that line the alveolar walls near the capillaries. Only their flattened nuclei can be recognized with certainty by light microscopy. Type II pneumocytes are cuboidal and occur singly or in small clusters between type I cells. They contain 0.2 to 1 micron wide multilamellar bodies that contain a high content of phospholipid that is the precursor to pulmonary surfactant, which interferes with the surface tension in the alveoli that would otherwise cause them to collapse. Club (Clara) cells are also thought to participate in the synthesis of surfactant. Type II cells serve as precursors to type I cells.
Where there are no capillaries, the alveolar septum contains fibroblasts, collagen, elastic fibers, smooth muscle cells, and macrophages known as dust cells. Also notable are alveolar pores, which equalize air pressure between the alveoli.
Circulatory System of the Lung
Branches of the pulmonary artery accompany the bronchi to the level of the respiratory bronchioles. From there they branch into an extensive network of capillaries suspended within the alveolar walls. Venules arising from these capillaries join in the intersegmental connective tissue and later empty into the pulmonary veins. Bronchi and connective tissue septa within the lung are vascularized by branches of the bronchial arteries, which are part of the systemic circulatory system. These two systems anastomose at the level of alveoli arising from the respiratory bronchioles.
Lab Guide questions (SUBMIT ANSWERS INDIVIDUALLY)
- Briefly describe the structural and functional differences between the following:
- Respiratory Bronchiole and Terminal Bronchiole
- Alveolar Sac and Alveolus
- Type I and Type II Pneumocyte
2. Trace the path of a molecule of oxygen from the nose to the bloodstream. Make sure to include all major airways, as well as each layer of tissue that must be traversed.
3. Describe the changes in the type of epithelia encountered as the molecule of oxygen in the question above moves from the nose to the alveolus.
4. How the the cartilage present along the Upper respirtory Tract and surfactants ensure that the airways will remain open under the normal conditions of inhalation and exhalation. How do these work?
IN GROUPS: Submit
IN SOFT COPIES AND HARD COPIES (6 PICTURES/LONG WHITE PAPER - preferably recycled paper)- Conducting Airway
- Conducting Epithelium
- Trachea
- Bronchus
- Intrapulmonary Air Conduits
- Bronchiole
- Respiratory Bronchioles
- Pneumocytes
- Pneumocytes EM
- Air-Blood Barrier
Urinary System Lab
Learning Objectives
- Distinguish the key microscopic components of the renal cortex and medulla
- Identify the structural components of the nephron
- Describe the structure of the surface across which filtration occurs
- Identify and distinguish the proximal tubule, distal tubule, and collecting duct
- Identify the component cells of the juxtaglomerular apparatus
- Name the important histological characteristics of the ureter, bladder, and urethra
- Describe some key pathological conditions associated with the kidney
- Distinguish the key microscopic components of the renal cortex and medulla
- Identify the structural components of the nephron
- Describe the structure of the surface across which filtration occurs
- Identify and distinguish the proximal tubule, distal tubule, and collecting duct
- Identify the component cells of the juxtaglomerular apparatus
- Name the important histological characteristics of the ureter, bladder, and urethra
- Describe some key pathological conditions associated with the kidney
Introduction
The urinary system is comprised of the kidney, ureter, urinary bladder, and urethra. The kidney produces urine, which contains excess water, electrolytes and waste products of the body. It then flows down the ureter into the bladder where it is temporarily stored. The bladder is then emptied via the urethra.
The urinary system is comprised of the kidney, ureter, urinary bladder, and urethra. The kidney produces urine, which contains excess water, electrolytes and waste products of the body. It then flows down the ureter into the bladder where it is temporarily stored. The bladder is then emptied via the urethra.
Kidney
The kidney has several important homeostatic, hormonal, and metabolic functions that include:
- The maintenance of water and electrolyte homeostasis
- Regulation of acid-base balance in conjunction with the respiratory system
- Excretion of metabolic waste products, especially the toxic nitrogenous compounds
- Production of renin for blood pressure control and erythropoietin, which stimulates red blood cell production in the bone marrow
- Conversion of vitamin D into active form for the regulation of calcium balance
The kidney is composed of an outer cortex and inner medulla. Portions of the medulla extend into the cortex as the medullary rays, collections of straight renal tubules. The medulla contains multiple cone-shaped lobes, known as medullary pyramids. These urinary lobes are fused in the cortex. The urine drains into the renal pelvis, which is the initial part of the ureter. The hilum of the kidney is the site of entry and exit for renal artery, renal vein, and ureter.
The kidney has several important homeostatic, hormonal, and metabolic functions that include:
- The maintenance of water and electrolyte homeostasis
- Regulation of acid-base balance in conjunction with the respiratory system
- Excretion of metabolic waste products, especially the toxic nitrogenous compounds
- Production of renin for blood pressure control and erythropoietin, which stimulates red blood cell production in the bone marrow
- Conversion of vitamin D into active form for the regulation of calcium balance
The kidney is composed of an outer cortex and inner medulla. Portions of the medulla extend into the cortex as the medullary rays, collections of straight renal tubules. The medulla contains multiple cone-shaped lobes, known as medullary pyramids. These urinary lobes are fused in the cortex. The urine drains into the renal pelvis, which is the initial part of the ureter. The hilum of the kidney is the site of entry and exit for renal artery, renal vein, and ureter.
Nephron
The nephron is the structural and functional unit of the kidney. There are about two million nephrons in each kidney. Nephrons begin in the cortex; the tubules dip down to the medulla, then return to the cortex before draining into the collecting duct. The collecting ducts then descend towards the renal pelvis and empty urine into the ureter.
The components of a single nephron include:
- renal corpuscle
- proximal convoluted tubule
- loop of Henle
- distal convoluted tubule
Different sections of nephrons are located in different parts of the kidney:
- The cortex contains the renal corpuscle, proximal, and distal convoluted tubules.
- The medulla and medullary rays contain the loops of Henle and collecting ducts.
Throughout the length of the nephron, capillaries called peritubular capillaries lie adjacent to all segments of the tubule. They originate from the efferent arteriole and are important for solute transport throughout the tubule.
The nephron is the structural and functional unit of the kidney. There are about two million nephrons in each kidney. Nephrons begin in the cortex; the tubules dip down to the medulla, then return to the cortex before draining into the collecting duct. The collecting ducts then descend towards the renal pelvis and empty urine into the ureter.
The components of a single nephron include:
The components of a single nephron include:
- renal corpuscle
- proximal convoluted tubule
- loop of Henle
- distal convoluted tubule
Different sections of nephrons are located in different parts of the kidney:
- The cortex contains the renal corpuscle, proximal, and distal convoluted tubules.
- The medulla and medullary rays contain the loops of Henle and collecting ducts.
Throughout the length of the nephron, capillaries called peritubular capillaries lie adjacent to all segments of the tubule. They originate from the efferent arteriole and are important for solute transport throughout the tubule.
Renal Corpuscle
The renal corpuscle is responsible for the filtration of the plasma. It contains two structures: the glormerulus and Bowman's capsule. The glomerulus is a cluster of capillary loops enclosed by Bowman's capsule, which is part of the renal tubule.
Bowman's capsule has two layers:
- The visceral layer is in contact with the glormerulus, and is composed of specialized epithelial cells known as podocytes.
- The parietal layer is the outer layer, and is composed of simple squamous epithelial cells. This layer is continuous with the epithelium of the proximal convoluted tubule.
The space between the two layers is named Bowman's space, and this space contains the ultrafiltrate of plasma. The plasma has to pass through a filtration barrier of three layers to enter Bowman's space: the capillary endothelium, the podocyte layer, and their fused basement membrane. Bowman's space is continuous with the proximal convoluted tubule.
Blood enters the renal corpuscle via afferent arterioles and then leaves via efferent arterioles. The part of renal corpuscle where afferent and efferent arterioles are located is known as the vascular pole. On the opposite end of the vascular pole is where the renal tubule begins and is known as the urinary pole.
Mesangial cells can also be found within the glomerulus. These cells secrete a matrix of basement membrane-like material to support the structure of the glomerulus.
The renal corpuscle is responsible for the filtration of the plasma. It contains two structures: the glormerulus and Bowman's capsule. The glomerulus is a cluster of capillary loops enclosed by Bowman's capsule, which is part of the renal tubule.
Bowman's capsule has two layers:
Bowman's capsule has two layers:
- The visceral layer is in contact with the glormerulus, and is composed of specialized epithelial cells known as podocytes.
- The parietal layer is the outer layer, and is composed of simple squamous epithelial cells. This layer is continuous with the epithelium of the proximal convoluted tubule.
The space between the two layers is named Bowman's space, and this space contains the ultrafiltrate of plasma. The plasma has to pass through a filtration barrier of three layers to enter Bowman's space: the capillary endothelium, the podocyte layer, and their fused basement membrane. Bowman's space is continuous with the proximal convoluted tubule.
Blood enters the renal corpuscle via afferent arterioles and then leaves via efferent arterioles. The part of renal corpuscle where afferent and efferent arterioles are located is known as the vascular pole. On the opposite end of the vascular pole is where the renal tubule begins and is known as the urinary pole.
Mesangial cells can also be found within the glomerulus. These cells secrete a matrix of basement membrane-like material to support the structure of the glomerulus.
Blood enters the renal corpuscle via afferent arterioles and then leaves via efferent arterioles. The part of renal corpuscle where afferent and efferent arterioles are located is known as the vascular pole. On the opposite end of the vascular pole is where the renal tubule begins and is known as the urinary pole.
Mesangial cells can also be found within the glomerulus. These cells secrete a matrix of basement membrane-like material to support the structure of the glomerulus.
Promixal Convoluted Tubule
The proximal convoluted tubule is the first segment of renal tubule. It begins at the urinary pole of the glomerulus. This is where the majority (65%) of the glomerular filtrate is reabsorbed. The convoluted portion of the tubule leads into a straight segment that descends into the medulla within a medullary ray and becomes the loop of Henle.
The proximal convoluted tubule is the first segment of renal tubule. It begins at the urinary pole of the glomerulus. This is where the majority (65%) of the glomerular filtrate is reabsorbed. The convoluted portion of the tubule leads into a straight segment that descends into the medulla within a medullary ray and becomes the loop of Henle.
Loop of Henle
The loop of Henle forms a hair-pin structure that dips down into the medulla. It contains four segments: the pars recta (the straight descending limb of proximal tubule), the thin descending limb, the thin ascending limb, and the thick ascending limb. The turn of the loop of Henle usually occurs in the thin segment within the medulla, and the tubule then ascends toward the cortex parallel to the descending limb. The end of the loop of Henle becomes the distal convoluted tubule near its original glomerulus. The loops of Henle run in parallel to capillary loops known as the vasa recta. Recall from Physiology that the loop of Henle serves to create high osmotic pressure in the renal medulla via the counter-current multiplier system. Such high osmotic pressure is important for the reabsorption of water in the later segments of the renal tubule.
The loop of Henle forms a hair-pin structure that dips down into the medulla. It contains four segments: the pars recta (the straight descending limb of proximal tubule), the thin descending limb, the thin ascending limb, and the thick ascending limb. The turn of the loop of Henle usually occurs in the thin segment within the medulla, and the tubule then ascends toward the cortex parallel to the descending limb. The end of the loop of Henle becomes the distal convoluted tubule near its original glomerulus. The loops of Henle run in parallel to capillary loops known as the vasa recta. Recall from Physiology that the loop of Henle serves to create high osmotic pressure in the renal medulla via the counter-current multiplier system. Such high osmotic pressure is important for the reabsorption of water in the later segments of the renal tubule.
Distal Convoluted Tubule
The distal convoluted tubule is shorter and less convoluted than the proximal convoluted tubule. Further reabsorption and secretion of ions occur in this segment. The initial segment of the distal convoluted tubule lies right next to the glomerulus and forms the juxtaglomerular apparatus.
The distal convoluted tubule is shorter and less convoluted than the proximal convoluted tubule. Further reabsorption and secretion of ions occur in this segment. The initial segment of the distal convoluted tubule lies right next to the glomerulus and forms the juxtaglomerular apparatus.
Juxtaglomerular Apparatus
The juxtaglomerular apparatus is a specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole. It is located near the vascular pole of the glomerulus. The main function of the apparatus is the secretion of renin, which regulates systemic blood pressure via the renin-angiotensin-alodosterone system. The juxtaglomerular apparatus is composed of:
- The macula densa, a collection of specialized epithelial cells of the distal convoluted tubule. These cells are enlarged as compared to surrounding tubular cells. The cells of the macula densa sense sodium chloride concentration in the tubule, which in turn reflects the systemic blood pressure.
- The juxtaglomerular cells of the afferent arterioles, which are responsible for secreting renin. These cells are derived from smooth muscles cells of afferent arterioles.
- The extraglomerular mesangial cells, which are flat and elongated cells located near the macula densa. Their function is currently unclear.
The juxtaglomerular apparatus is a specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole. It is located near the vascular pole of the glomerulus. The main function of the apparatus is the secretion of renin, which regulates systemic blood pressure via the renin-angiotensin-alodosterone system. The juxtaglomerular apparatus is composed of:
- The macula densa, a collection of specialized epithelial cells of the distal convoluted tubule. These cells are enlarged as compared to surrounding tubular cells. The cells of the macula densa sense sodium chloride concentration in the tubule, which in turn reflects the systemic blood pressure.
- The juxtaglomerular cells of the afferent arterioles, which are responsible for secreting renin. These cells are derived from smooth muscles cells of afferent arterioles.
- The extraglomerular mesangial cells, which are flat and elongated cells located near the macula densa. Their function is currently unclear.
Collecting Ducts
The terminal portion of the distal tubule empties through collecting tubules into a straight collecting duct in the medullary ray. The collecting duct system is under the control of antidiuretic hormone (ADH). When ADH is present, the collecting duct becomes permeable to water. The high osmotic pressure in the medulla (generated by the counter-current multiplier system/loop of Henle) then draws out water from the renal tubule, back to vasa recta.
The terminal portion of the distal tubule empties through collecting tubules into a straight collecting duct in the medullary ray. The collecting duct system is under the control of antidiuretic hormone (ADH). When ADH is present, the collecting duct becomes permeable to water. The high osmotic pressure in the medulla (generated by the counter-current multiplier system/loop of Henle) then draws out water from the renal tubule, back to vasa recta.
Renal Pelvis and Ureter
Numerous collecting ducts merge into the renal pelvis, which then becomes the ureter. The ureter is a muscular tube, composed of an inner longitudinal layer and an outer circular layer. The lumen of the ureter is covered by transitional epithelium (also called urothelium). Recall from the Laboratory on Epithelia that the transitional epithelium is unique to the conducting passages of the urinary system. Its ability to stretch allows the dilation of the conducting passages when necessary. The ureter connects the kidney and the urinary bladder.
Numerous collecting ducts merge into the renal pelvis, which then becomes the ureter. The ureter is a muscular tube, composed of an inner longitudinal layer and an outer circular layer. The lumen of the ureter is covered by transitional epithelium (also called urothelium). Recall from the Laboratory on Epithelia that the transitional epithelium is unique to the conducting passages of the urinary system. Its ability to stretch allows the dilation of the conducting passages when necessary. The ureter connects the kidney and the urinary bladder.
Urinary Bladder
The ureter empties the urine into the bladder. The transitional epithelium continues over the surface of this organ. The thickened muscular layers become interwoven and cannot be clearly identified at this point.
The ureter empties the urine into the bladder. The transitional epithelium continues over the surface of this organ. The thickened muscular layers become interwoven and cannot be clearly identified at this point.
Urethra
The urethra carries the urine away from the bladder to the outside of the body. In the male, it is joined by the genital system. The epithelium changes from transitional to stratified or pseudostratified columnar in the urethra, and to stratified squamous in the distal end of the urethra.
The urethra carries the urine away from the bladder to the outside of the body. In the male, it is joined by the genital system. The epithelium changes from transitional to stratified or pseudostratified columnar in the urethra, and to stratified squamous in the distal end of the urethra.
Lab Guide questions (SUBMIT ANSWERS INDIVIDUALLY)
| Proximal Tubule | A. filters the plasma |
| Distal Tubule | B. most reabsorption occurs here |
| Loop of Henle | C. generates countercurrent gradient |
| Collecting Duct | D. site of action of ADH |
| Renal Corpuscle | E. cells from the juxtaglomerular apparatus |
- Podocyte
- Mesangial Cell
- Macula Densa
- Juxtaglomerular Complex
3. Describe the changes in the epithelium as urine moves from the ureter through the urethra.
IN GROUPS: Submit
IN SOFT COPIES AND HARD COPIES (6 PICTURES/LONG WHITE PAPER - preferably recycled paper)- Kidney
- Renal Corpuscle
- Renal Corpuscle 2
- Podocyte EM
- Podocyte Scanning EM
- Filtration Barrier
- Proximal Convoluted Tubule
- Proximal Convoluted Tubule EM
- Loop of Henle
- Distal Convoluted Tubule
- Juxtaglomerular Apparatus
- Collecting Ducts
- Renal Pelvis
- Ureter
- Urinary Bladder
Skin Lab
Learning Objectives
- Name and distinguish the four layers of the epidermis in terms of structure and function.
- Identify the two layers of the dermis and the hypodermis and explain their functional significance.
- Describe the basic structure and function of several key epidermal derivatives.
- Contrast the three modes of exocrine secretion and give examples of cells that exhibit each type.
- Describe the structure of the mammary glands.
- Recognize some key pathological examples affecting skin and epidermal derivatives.
Introduction
The skin is the largest organ of the body and varies greatly in different regions. It has five main functions: protection, thermoregulation, sensation, metabolic functions (vitamin D, adipose metabolism), and sexual attraction.
Skin is composed of several subunits. The three main divisions are:
Skin is composed of several subunits. The three main divisions are:
- the epidermis, or surface epithelium, which is a self-regenerating stratified squamous epithelium that produces a protective protein layer of keratin.
- the dermis, an underlying layer of dense collagenous connective tissue that contains hair follicles, sweat glands, blood and lymphatic vessels, sensory receptors and nerves, and connective tissue cells.
- the hypodermis, another connective tissue layer that is rich in white adipose cells and contains large blood vessels that supply the smaller vessels of the dermis.
Epidermis
The epidermis is a stratified squamous epithelium that contains discrete layers of proliferating, differentiating, and differentiated cells called keratinocytes. It is divided into four layers that have different structural appearances:
- Basal Cell Layer - Keratinocytes begin in the deepest layer of the epidermis, the stratum basale, which is a row of columnar cells resting on the basal lamina that separates the epidermis from the dermis. Mitosis occurs exclusively at the basal cell layer and allows for the replacement of cells lost from the surface.
- Stratum Spinosum - After forming in the basal cell layer, keratinocytes migrate upwards into the stratum spinosum. In this layer, they develop short projections that attach via desmosomes to adjacent cells. The stratum spinosum is also known as the "prickly layer" because of these characteristic spines. The cells in this layer produce cytokeratin, an intermediate filament precursor to keratin.
- Stratum Granulosum - The third layer is the stratum granulosum. In this layer, the keratinocytes have become squamous cells that contain granules of keratohyaline, a precursor to the extracellular keratin that protects the skin tissue from abrasion.
- Stratum Corneum - The most superficial layer of the epidermis is the aceullar stratum corneum. It is the most functionally important layer of the skin and consists of flat, keratinized scales that are shed and replaced continuously. This is the layer that includes the final keratin product, which is a combination of cytokeratin and keratohyaline.
Recall from the Laboratory of Epithelia that epithelia differ in their degree of keratinization - those exposed to abrasion and desiccation are heavily keratinized, but those that form mucous membranes do not have much keratin. For example, the skin is highly keratinized, but the esophagus, anal canal,and vagina are not. Instead of protection by keratin, these mucous membranes are kept moist by glandular secretions. Mucous membranes lack a stratum granulosum and stratum corneum.
The epidermis contains several characteristic cell types:
- Melanocytes occur at intervals among the basal keratinocytes and produce melanin pigment, which is most abundant in sun-exposed skin and in areas surrounding body openings. Melanin is synthesized from tyrosine and transferred as melanin granules to the surrounding epithelial cells. While the number of melanocytes is the same in light- and dark-skinned people, they are far more active in the latter.
- Langerhans cells are typically located in the stratum spinosum and are the equivalent of macrophages in the skin tissue.
- Merkel cells are attached to keratinocytes by desmosomes and are most commonly found in highly sensitive areas like the fingertips - these serve as touch receptors.
Dermis and Hypodermis
The dermis consists of two layers:
- Papillary layer - The most superficial layer of the dermis is the papillary layer, which consists of loose connective tissue immediately beneath the epidermal basement membrane.
- Reticular layer - The reticular layer is composed of dense, irregular collagenous connective tissue.
Most blood vessels, nerves, and sensory receptors occur in the papillary layer. This region also contains Meissner's corpuscles, which sense light touch.
The hypodermis is the fatty layer beneath the dermis. It is thickest in the abdominal wall and virtually absent in the eyelid, scrotum, penis, and the dorsal side of the hand. This layer contains a significant number of fibroblasts, which synthesize collagen and elastin. The hypodermis contains Pacinian corpuscles, which sense deep touch.
The hypodermis is the fatty layer beneath the dermis. It is thickest in the abdominal wall and virtually absent in the eyelid, scrotum, penis, and the dorsal side of the hand. This layer contains a significant number of fibroblasts, which synthesize collagen and elastin. The hypodermis contains Pacinian corpuscles, which sense deep touch.
Epidermal Derivatives
Many structures are derived from epidermal tissue. Keep in mind that just because a structure is derived from the epidermis does not mean that it is located in the epidermis.
Hair follicles are encased by an invagination of the epidermis into the dermis known as the external root sheath. They contain specially organized keratin built into long tubular structures. Remember that hair follicles have generous blood and nerve supplies. There are three states of hair follicles:
Hair follicles are encased by an invagination of the epidermis into the dermis known as the external root sheath. They contain specially organized keratin built into long tubular structures. Remember that hair follicles have generous blood and nerve supplies. There are three states of hair follicles:
- Anagen - Growing follicles synthesize hair. They are long and most numerous in the scalp.
- Catagen - Resorbing follicles are in a short phase of regression that signals the end of active hair growth.
- Telogen - Resting follicles contain a fully formed hair.
- Eccrine sweat glands occur throughout most of the skin.
- Apocrine sweat glands are much larger than eccrine glands and produce a thicker secretion.
Mammary Glands
Mammary glands are one of the most complex epidermal derivatives. These glands are present in both sexes, but only develop fully in females after parturition. They begin to undergo dramatic structural changes at puberty.
The basic structure of the mammary glands involves alveoli that contain two layers of cells: an inner cuboidal epithelium and an outer layer of myoepithelial cells. The alveoli make up tubuloalveolar glands, or lobes, which connect via lactiferous ducts to the base of the nipple. After milk is produced, it is secreted and travels through the ducts into spindle-shaped enlargements beneath the areola known as lactiferous sinuses.
Important structural changes occur in the mammary glands over the course of the female's lifetime:
The basic structure of the mammary glands involves alveoli that contain two layers of cells: an inner cuboidal epithelium and an outer layer of myoepithelial cells. The alveoli make up tubuloalveolar glands, or lobes, which connect via lactiferous ducts to the base of the nipple. After milk is produced, it is secreted and travels through the ducts into spindle-shaped enlargements beneath the areola known as lactiferous sinuses.
Important structural changes occur in the mammary glands over the course of the female's lifetime:
- In a nonpregnant, sexually mature female, the glandular tissue consists of ducts with small terminal alveoli embedded in an abundant connective tissue stroma that contains many adipose cells.
- During pregnancy, hormonal stimulation results in the proliferation of the intralobar ducts and terminal alveoli. The epithelial cells become enlarged and vacuolated, as milk fat production increases.
- After parturition, the gland enters its active secretory phase and produces watery milk containing membrane-bound lipid droplets, as well as milk proteins, lactose, and cellular debris.
- Suckling causes release of prolactin from the anterior pituitary and oxytocin from the posterior pituitary (processes that you will study in detail during Physiology). Prolactin maintains milk production and oxytocin causes the contraction of myoepithelial cells and ejection of milk.
Types of Exocrine Secretion
In your study of Histology, you may hear three different terms to describe exocrine cells. These can often be confusing.
- Merocrine, or eccrine, secretion occurs by exocytosis. This is the mode of secretion of both eccrine and apocrine glands, which can be very confusing.
- Apocrine secretion occurs when a portion of the plasma membrane containing the secretion buds off from the cell. This is the mode of secretion of the mammary glands and mucous-producing cells, but not the apocrine sweat glands.
- Holocrine secretion occurs when the entire cell disintegrates in order to release its secretion. Sebaceous glands exhibit holocrine secretion, as the sebum is released with remnants of dead cells.
Pre-Lab Guide questions (SUBMIT ANSWERS IN PAIRS)
(Yellow pad to be submitted on 3-8-17)
- Name the four layers of the epidermis and the state of keratin associated with each.
- What are the important differences between sebaceous glands, eccrine sweat glands, and apocrine sweat glands?
- What is the structure of the mammary gland, and what key differences do you expect to see between active and inactive mammary tissue?
- Name the three types of exocrine secretion, their key characteristics, and an example of a cell that demonstrates each one.
ASSIGNMENT/TAKE HOME ACTIVITY:
IN GROUPS: SUBMIT PHOTOMICROGRAPHS OF THE FOLLOWING ON FRIDAY (3-10-17) - IN SOFT COPIES AND HARD COPIES (6 PICTURES/LONG WHITE PAPER - preferably recycled paper)
LABEL THE SPECIFIC PARTS OF EACH:
- Skin
- Epidermis
- Stratum Basale and Stratum Spinosum
- Stratum Basale and Stratum Spinosum EM
- Stratum Granulosum and Stratum Corneum
- Melanocytes and Langerhans Cells
- Pacinian Corpuscle
- Meissner's Corpuscle
- Hair
- Hair Follicle
- Sebaceous Glands
- Eccrine Sweat Glands
- Apocrine Sweat Glands
- Inactive Mature Breast
- Active Mature Breast
- Breast Acini
MUST STUDY all the pictures before attending the lab. A POST LAB QUIZ WILL BE GIVEN.
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