CTO Post Quiz #5 Material Flashcards
(142 cards)
1
Q
What is a meant by a lobe of the kidney?
A
A kidney LOBE (not lobule) consists of a medullary pyramid, cortex and half of the renal columns on either side.
2
Q
If you looked at a medullary ray under the microscope, what would be the dominant feature?
A
A mecullary ray contains collecting tubules.
3
Q
What does the cortical labyrinth consist of?
A
The cortical labyrinth consists of renal corpuscles and convoluted tubules.
4
Q
Follow the course of blood through the kidney from the renal artery to the renal vein.
A
The renal blood supply goes from the renal artery to the segmental arteries, to the interlobar arteries, to the arcuate arteries, to the interlobular arteries, to the afferent arterioles, to the glomerular capillaries, to the efferent arterioles to the cortical capillary plexus. From here, blood can drain to the interlobular veins or to the vasa rectae. Both the interlobular arteries and the vasa rectae connect into to the arcuate veins, which convey blood to the interlobar veins, which drain into the renal veins.
5
Q
Where does the capillary plexus in the cortical labyrinth come from?
A
The capillary plexus around the convoluted tubules arises comes from efferent arterioles.
6
Q
What is unusual about the embryonic development of the nephron and the collecting ducts?
A
The components of the nephron and the collecting ducts have different embryonic origins and must connect during embryogenesis.
7
Q
Which tubules in the cortex are located primarily in between lobules of the kidney?
A
Collecting ducts are located mostly in the area in between lobules of the cortex.
8
Q
Where are renal corpuscles located in the cortex?
A
85% of renal corpuscles are in the upper cortex, while 15% are juxtamedullary.
9
Q
What is different between the uriniferous tubules of juxtamedullary renal corpuscles?
A
The juxtamedullary renal corpuscles have longer loops of Henle, extending deeper into the renal medulla.
10
Q
What is the barrier between the blood and the urinary space (Bowman’s space) in the renal corpuscle?
A
The barrier consists of fenestrated endothelium, a basement membrane, and podocytes with filtration slits between pedicles.
11
Q
What is the structure of the visceral layer of Bowman’s membrane? The parietal?
A
The visceral layer consists of podocytes; the parietal layer consists of simple squamous cells.
12
Q
What is the function of mesangial cells?
A
Mesangial cells clean deposited proteins off of the basement membrane of the glomeruli.
13
Q
What is unusual about the basement membrane of the glomerulus?
A
The basement membrane has charged proteins and proteoglycans to filter big proteins.
14
Q
What is the progression of filtrate through the uriniferous tubules?
A
Filtrate progress through proximal convoluted tubules, thick descending limbs (of Henle), thin descending limb, thin ascending limb, thick ascending limb and the distal convoluted tubule. This ends in a collecting tubule that connects to a collecting duct.
15
Q
What is the structure of the wall of the distal convoluted tubules?
A
The DCT consists of simple cuboidal epithelium without a brush border.
16
Q
On H&E stain, how can you distinguish PCT from DCT?
A
The cells of the PCT are redder (more eosinophilic) and taller than the cuboidal cells of the DCT. Also the cells of the PCT have microvilli.
17
Q
What is the structure of proximal convoluted tubules?
A
The PCT consists of simple cuboidal epithelium with a brush border.
18
Q
A renal lobule is defined by:
A
All of the nephrons that drain into a collecting duct.
19
Q
What is the structure of descending and ascending thin limbs (of Henle)?
A
They are comprised of simple squamous epithelium.
20
Q
Why are the thin decending and ascending limbs adjacent to one another?
A
This allows countercurrent exchange of sodium to prevent dilution of the sodium concentration in the renal medulla.
21
Q
What is the function of the thick limb of Henle?
A
It is impermeable to water but pumps sodium to produce a high sodium concentration in the renal medulla.
22
Q
What is the structure of the collecting ducts?
A
Collecting ducts are lined by cuboidal epithelium with prominent infoldings of lateral cell borders.
23
Q
What hormone has the most powerful influence on collecting ducts?
A
Collecting ducts are affected by anti-diuretic hormone (ADH) that allows water to escape from the collecting duct into the medulla of the kidney, where it is picked up by the vasa rectae.
24
Q
What are the components of the juxtaglomerular apparatus?
A
The JGA consists of several compnents. The macula densa, which is a specialization of the DCT that detects Na+ and fluid levels. Juxtaglomerular cells (JG) are modified smooth muscle cells that secrete renin. Extraglomerular mesangial cells have a function that is not well understood.
25
What do JG cells secrete and how do they affect the body?
JG cells secrete rennin, which converts angiotensinogen to angiotensin I. This, in turn, is converted to angiotensin II by angiotensin converting enzyme. Angiotensin II has effects on blood vessel contraction and on secretion of aldosterone from the adrenal cortex. This hormone, in turn, causes blood volume elevation by fluid retention at the DCT.
26
What is the pathway for urine from the medullary pyramid outward?
Collecting ducts open onto the renal papilla, which empties urine into the minor calyx, to the major calyx, to the renal pelvis, to the ureter, to the urinary bladder and finally out the urethra.
27
What is the epithelium that lines the lower urinary tract?
It is transitional epithelium (urothelium), which changes shape (flattens) when the system is distended. These cells have prominent terminal bars.
28
What are the layers of the ureter?
The mucosa is on a thick lamina propria. It has no submucosa. There is a thick muscularis, but layers are not distinct. There is an adventitia outside.
29
What is the structure of the urinary bladder?
It has a lining of transitional epithelium on a lamina propria. There is no submucosa but a thick smooth muscle layer. Outside is an adventitia.
30
What does the immune system do?
The immune system is responsible for the defense of the body against the limitless array of potential pathogens and other foreign material (macromolecules, microorganisms, viruses, transformed cells, etc.) that we encounter on a daily basis.
31
What are the components of the innate immune system?
The innate (native, natural) immune system is provided by epithelial barriers and their secretions, and by a host of cells (macrophages, granulocytes, natural killer (NK) cells, etc) that can destroy or remove foreign elements by means of non-specific, stereotypical mechanisms.
32
What is the specific immune system?
The specific (adaptive, acquired) immune system is provided by B-lymphocytes (B-cells) and T lymphocytes (T-cells), which mediate a very specific humoral (antibody-mediated) or cell-mediated immune response respectively. Cooperation between the innate and the specific immune system is the rule, and both humoral and cell-mediated responses may work together in the defense of the organism.
33
What provides the specificity of the adaptive immune system?
The specificity of the adaptive immune system is provided by immunoglobulins (antibody) or by T-cell receptors (TCRs), each of which has the ability to recognize one of potentially billions of different foreign molecules.
34
What molecules mark the cell as “self”?
The recognition of 'self' is mediated by the human leukocyte antigen (HLA) complex (major histocompatability complex; MHC).
35
Where would you find MHC I?
MHC I is a receptor molecule that is a transmembrane protein found on virtually all nucleated cells. MHC I displays antigens (normal or abnormal) produced inside those cells.
36
Where would you find MHC II?
MHC II is a transmembrane receptor found on antigen presenting cells (APCs) that is specifically designed for displaying exogenous foreign antigens and “presenting” them to the lymphocytes.
37
How do B-cells recognize antigens?
B-cells recognize antigen by means of surface-bound immunoglobulins (Igs).
38
What are the types of antibodies?
Several types of immunoglobulins (antibodies) exist (IgM, IgD, IgG, IgE, IgA).
39
What are the fundamental units of all antibodies?
All antibodies share a common basic structure, which includes two heavy chains and two light chains (which come together to form an Fc [constant] region) and an antigen-binding region, the Fab domain.
40
During maturation, what are the initial antibodies on a B-cell?
IgM and IgD represent the initial B-cell surface immunoglobulins.
41
What are the first antibodies secreted by a recently formed plasma cell?
The first soluble antibodies secreted by a plasma cell are low affinity IgMs.
42
What is isotype switching?
Cells resulting from the clonal expansion of the original B-cell will undergo affinity maturation and isotype switching resulting in the secretion of higher affinity antibodies (IgG, IgE or IgA). IgG is the predominant Ig found in blood; IgA is, overall, the most abundantly produced of the Igs and is found in many bodily secretions (saliva, mucous, breast milk); IgE is associated with molecules typically considered allergens.
43
What provides the specificity of the T-cell response?
The T-cell receptor provides the antigen specificity for the T-cell response.
44
What are the MHC-I restricted T-cells?
MHC I restricted T-cells are CD8+ cytotoxic lymphocytes (CTLs).
45
What are the MHC II restricted T-cells?
MHC II-restricted T-cells are CD4+ TH cells.
46
What is the usual process of a humoral immune response?
A humoral immune response is usually initiated by the binding of antigen to the membrane-bound immunoglobulins on the surface of a B-cell. That antigen will be processed by the B-lymphocyte and then presented in association with MHC II to a TH cell. The release of cytokines by the T-cell will then trigger a clonal expansion of that B-cell into plasma cells and memory B cells.
47
How are NK cells involved in the humor response?
Antibodies may be used for opsonization of foreign cells and their subsequent destruction by phagocytosis or NK cell-mediated lysis.
48
How are macrophages involved in the immune response?
Exogenous antigens can be phagocytosed and processed by macrophages (or other APCs), which then present that antigen in the company of MHC II to TH cells. This triggers proliferation of that particular TH cell (to yield additional TH cells including memory cells) as well as the secretion of cytokines to stimulate increased macrophage activity. This may also activate appropriate B-cells, which is why we now recognize the mutual interactions of humoral and cell-mediated immunity.
49
How are abnormal cells (including those infected by viruses) recognized?
Endogenously produced antigens (e.g. produced by virus-infected cells or tumor cells) will be expressed on the cell surface in association with the MHC I complex. These antigens are recognized by the CD8+ CTLs, which are then activated, resulting in proliferation, memory cell production and cytokine secretion.
50
How do cytotoxic lymphocytes kill target cells?
Cytotoxic lymphocytes kill target cells by the secretion of lytic agents (e.g. perforins, granzymes).
51
Inside the capsule of the thymus, what are the portions of the thymic parenchyma?
There is a cortex and a medulla of the thymus.
52
What makes up the stroma of the thymus?
The epithelioreticular cells (ERC) are the stroma of the thymus. There is no connective tissue within the thymus.
53
What happens to the thymus in adulthood?
It becomes a fatty, involuted structure in the adult.
54
What is the function of the thymic cortex?
The thymic cortex has positive selection. Thymocytes that bind strongly to MHC I are selected and allowed to proceed to mature in the medulla. Those that don't recognize self are signaled to undergo apoptosis.
55
What is the function of the thymic medulla?
Thymocytes that recognize and react against self MHC I are selected against and triggered to undergo apoptosis. If they are not adequately screen out, these thymocytes may result in autoimmune disease.
56
What is the function of the epithelial reticular cells?
These are associated with thymocyte differentiation and selection. They secrete a large number of thymic hormones. They provide selection barriers that prevent all but certain cells from entering the thymus. ERC I are the blood-thymic barrier. ERC II express MHC I and II and are the cells that positively select thymocytes. ERC III cells are the barrier between cortex and medulla. ERC IV are on the medullary side of the cortico-medullary junction and ERC V have both MHC I and II and are the negative selecting cells. Finally ERC VI are the cells that make Hassall's corpuscles.
57
What are Hassall's corpuscles?
In the thymic medulla, Hassall's corpuscles, comprised of keratinized type VI epithelial reticular cells, are a common morphological entity (especially in aged thymus) and aid in the histological identification of thymus.
58
What are the functions of lymph nodes?
Lymph nodes are an encapsulated secondary lymphoid organ that serves as a 'filter' for antigens traveling within the lymphatic circulation.
59
How do afferent lymphatics enter the lymph node and how does lymph traverse the node?
Afferent lymphatics pierce the capsule of the node and deliver lymph first into a subcapsular sinus. Lymph then follows a series of leaky lymphatic sinusoids that allow for the percolation of the lymph down through the cortex, the subjacent paracortex, and finally into the medulla of the node where medullary cords of lymphoid cells are surrounded by a network of medullary sinuses. The sinuses then coalesce to form the efferent lymphatic vessels that leave the node at its hilum.
60
Where in the node would you expect to find metastatic cells if they are metastasizing via the lymph?
Metastatic cells would tend to lodge in the subcapsular sinus.
61
Where do you find lymphoid follicles in the lymph node?
The B-cell-dependent lymphoid follicles (nodules) are found in the cortex.
62
What are the characteristics of secondary lymphoid follicles?
Primary follicles contain naïve lymphocytes, which, upon encountering their specific antigen, will become activated (i.e. proliferate, convert into plasma cells, etc). This activation can be seen by a clearing of the central portion of the follicle to form a germinal center, the hallmark of a secondary follicle.
63
What is the function of follicular dendritic cells?
A population of follicular dendritic cells serves to sequester antigen and optimize the potential for lymphocyte-antigen interaction. These are a type of antigen presenting cell.
64
What is the paracortex of the lymph node?
The paracortex is a T-cell dependent area immediately below the cortical follicles.
65
What is unusual about blood vessels in the paracortical region of the lymph node?
The high-endothelial venules are found within the paracortical region. Lymphocytes leave the blood stream and enter the lymphatic circulation via these HEVs.
66
What would you expect to find in the medullary cords?
The medullary cords consist of a loose arrangement of lymphocytes, plasma cells, macrophages and supportive reticular cells.
67
What is the function of the spleen?
The spleen acts as an immunological filter for the blood.
68
What are the histologic parts of the splenic parenchyma?
The spleen is surrounded by a capsule and is organized into regions of red pulp and white pulp.
69
What would you find in red pulp?
You would find splenic sinuses and diffuse lymphoid tissue containing macrophages, and reticular connective tissue in the red pulp. There would be large number of red blood cells.
70
What is white pulp?
White pulp consists of aggregates of lymphocytes. These are organized into lymphoid follicles and the PALS (periarteriolar lymphoid sheaths).
71
Describe the circulation of the spleen.
Large blood vessels enter the substance of the spleen via connective tissue trabeculae. Upon leaving the trabeculae, central arteries (arterioles) become ensheathed in a layer of T-cells (the periarteriolar lymphatic sheath - PALS). Lymphoid follicles (B-cells) may be seen associated with (and distorting) the PALS. Branches from the central arteries, called penicillar arteries distribute to the splenic parenchyma. Many of these end by opening into the red pulp. The splenic sinuses have a unique architecture (barrel-stave endothelium with surrounding reticular fibers) that serve as a cellular sieve to filter out aged blood cell
72
What is meant by “open circulation”?
This means that the penicillar arterioles open into the splenic parenchyma, pouring blood into the red pulp. However, some of these arterioles may have direct continuity with the venous sinuses (closed circulation).
73
How do blood cells get into the veins?
Red blood cells, for example, must pass between discontinuous endothelium (stave cells) that form slits along the wall of the splenic sinuses. These cells also must pass a discontinuous basement membrane that surrounds the sinus like hoops around a barrel. Those that cannot pass are broken down.
74
What is “mucosal-associated lymphoid tissue” and where do you find it?
Mucosal-associated lymphoid tissue (MALT) is typically found beneath epithelial surfaces that are common sites of antigen entry (e.g. GI tract, respiratory tract, etc). This may consist of diffuse lymphoid tissue, occasional lymphoid nodules, or aggregates of nodules such as is seen in the Peyer's patches of the ileum or in the tonsils.
75
What is the outermost layer of the ovary?
The surface of the ovary is covered by the germinal epithelium (modified peritoneal layer) that is mostly cuboidal epithelium.
76
What is the thick connective tissue layer that surrounds the parenchyma of the ovary called?
The entire ovary is encased within a connective tissue capsule called the tunica albuginea.
77
Where in the ovary would you find the various stages of the female gamete?
The cortex of the ovary is the site of generation of the female gamete or ovum (including developing follicles [oocyte + supportive cells] and surrounding stromal cells.
78
In what phase of replication are primary oocytes arrested?
Primary oocytes are arrested in prophase of meiosis I until puberty or beyond.
79
What surrounds the oocyte when it is in a primary follicle?
The oocyte secretes the constituents of the zona pellucida which surrounds it until well after fertilization.
80
What is the difference in appearance between a primordial and a primary follicle?
The primordial follicle is surrounded by flattened, squamous-appearing epithelial cells and no evident zona pellucidum. In the primary follicle, there is a prominent zona pellucidum and a single layer of cuboidal granulosa cells.
81
What hormone stimulates a cohort of primary follicles to mature?
The further development of a cohort of preantral follicles will be stimulated each month by follicle stimulating hormone (FSH) and secondary (antral) follicles will be formed.
82
What is the main product of the granulosa cells of the antral follicle and what causes them to produce this?
With stimulation by both FSH and luteinizing hormone (LH), the granulosa cells, working together with a population of modified stromal cells, the theca interna, will begin producing estrogens.
83
What is the appearance of the Graafian follicle?
The fully mature, Graafian follicle is characterized by a large antrum filled with the liquor folliculi, and containing an oocyte within a collection of granulosa cells, the cumulus oophorus. The granulosa cells surrounding the oocyte are the corona radiata.
84
What is the main trigger for the “LH surge”?
Increasing levels of estrogen result in an LH surge which then triggers the completion of meiosis I and the process of ovulation. Typically only one of the cohort of antral follicles will be ovulated
85
What happens to the other Graafian follicles that have matured but not ovulated during the cycle?
The remainder of the follicles will undergo degeneration into atretic follicles (corpora fibrosa).
86
What happens to the follicle immediately after ovulation?
Following ovulation, the remnant of the follicle will be converted into a corpus luteum (CL). This has two components, a granulosa lutein and a theca lutein. Residual LH will stimulate these cells to produce progesterone (and some estrogen).
87
What happens to the corpus luteum if fertilization does not take place?
In the absence of pregnancy, the corpus luteum will degenerate into a corpus albicans and the ovarian cycle will begin again.
88
What is the main stimulus for the proliferative phase of the endometrium?
Estrogen from the maturing follicles stimulates the proliferative phase of the endometrial cycle.
89
What happens to the endometrium during the proliferative phase of the menstrual cycle?
During the proliferative phase of the endometrium, endometrial tissues, both epithelial tissues and stromal cells, are mitotically active. This results in the development of a thick stratum functionalis layer from the underlying stratum basalis.
90
What is the main stimulus for the secretory phase of the endometrium?
Progesterone from the corpus luteum leads to the secretory phase.
91
What happens during the secretory phase of the endometrium?
The endometrial glands begin production of glycogen-rich secretions in anticipation of nourishing an implanted embryo.
92
What triggers menstruation?
In the absence of pregnancy, estrogen and progesterone levels drop. This results in contraction of the spiral arteries supplying the endometrium, leading to the necrosis of the stratum functionalis and its sloughing during the menstrual phase.
93
At what stage is the oocyte at the time of ovulation?
Ovulation marks the completion of meiosis I and the formation of a secondary oocyte (i.e., becomes haploid).
94
What happens to the cell cycle of the secondary oocyte?
It arrests in the prophase of Meiosis II and will only finish this if it is fertilized.
95
How is the oocyte moved through the uterine tube?
Both ciliary action and peristaltic waves generated by the smooth muscle layers of the oviduct help propel the egg through the isthmus, into the intramural portion of the oviduct and finally into the uterine cavity. The mucosa of the oviduct, especially the distal end, is thrown into numerous folds, and is covered by a ciliated, simple columnar epithelium that sweep toward the uterine cavity. At the time of ovulation, the secondary oocyte is usually swept into the fimbriated end or infundibulum of the oviduct and then into its ampulla.
96
What is the function of “peg” cells?
A population of secretory peg cells provided some nutritive secretions.
97
Where does fertilization usually take place?
Fertilization usually occurs in the distal segment of the oviduct when a spermatozoon penetrates the protective layer of granulosa cells and then enzymatically digests its way through the zona pellucida (the function of acrosomal enzymes). This allows for the fusion of the egg and sperm membranes.
98
What prevents polyspermia?
Penetration of the oocyte by the sperm triggers a calcium flux in the oocyte resulting in discharge of cortical granules, producing a block to polyspermy.
99
When does implantation of the blastocyst usually take place?
Implantation of the blastocyst into the endometrium usually occurs by day 7 (post-fertilization).
100
Where is the most common location of ectopic implantation?
Ectopic implantation most commonly occurs in the oviduct (tubal pregnancy).
101
What cells of the blastocyst invade the endometrium?
The syncytiotrophoblast layer leads invasion of the endometrium by the blastocyst.
102
What cells produce hCG and why is it important?
The production of human chorionic gonadotropin (hCG) by the syncytiotrophoblast is essential to the survival of the implanted embryo. This hormone provides continued stimulation of the corpus luteum (now a CL of pregnancy), and thus continued maintenance of the endometrium (now called the decidua). In subsequent weeks, the placenta will also become an important source of other hormones (e.g. estrogen, progesterone) necessary for normal gestation.
103
What is the histologic structure of the cervix?
The uterine cervix is characterized by a dense fibromuscular stroma that maintains the narrow opening of the cervix and prevents fetal loss until it is softened late in pregnancy by the action of hormones. There is also a secretory mucosal layer responsible for the production of cervical mucus, the consistency of which changes during the menstrual cycle. The simple columnar epithelium of the endocervix gives way to a stratified squamous epithelium where the ectocervix is exposed to the vaginal environment.
104
What is important about the site of transition from simple columnar to stratified squamous epithelium in the cervix?
The transformation zone where metaplasia occurs is the common site of development of cervical cancer, but dysplastic or neoplastic cell growth at this site can be readily monitored by means of Pap smears.
105
What kind of epithelium lines the vagina?
The vagina is lined by a stratified squamous non-keratinized epithelium. The cells of the lining show changes during the monthly cycle, most notably in the quantity of glycogen produced by the cells.
106
Are there any glands in the vagina?
Glands are lacking in the vaginal mucosa.
107
What comprises the remainder of the walls of the vagina?
The walls of the vagina are supported by a well-vascularized fibroelastic connective tissue, smooth muscle, and, at some levels, skeletal muscle from the urogenital diaphragm.
108
What comprises the histologic structure of the labia majora and minora?
The vulva includes the labia majora and labia minora, both folds of skin containing sebaceous and sweat glands. The hair follicles and adipose tissue of the labia majora are not found in the labia minora.
109
What is the histologic structure of the clitoris?
The clitoris represents a body of erectile tissue, comprised of a network of large, endothelial-lined sinuses supported by a network of fibromuscular trabeculae and surrounded by a thick connective tissue capsule (the tunica albuginia).
110
What is the connective tissue capsule surrounding each testis called?
The tunica albuginea.
111
What is a lobule of the testis?
Each testis is comprised of ~ 250 lobules separated by incomplete connective tissue septa. Each lobule contains 1-4 seminiferous tubules.
112
What is the shape of seminiferous tubule?
These are convoluted loops, that connect at each end to tubules that convey sperm toward the epididymis (roughly “U” shaped).
113
What are the primitive germ cells of the epithelium of the seminiferous tubule called, and where are they located?
They are called spermatogonia and they rest on the basal lamina.
114
What are the products of mitotic division of the primitive germ cells in the seminiferous tubules?
At puberty the spermatogonia begin to divide. Their daughter cells will either remain as stem cell spermatogonia or become progenitor spermatogonia, which will continue to divide and then differentiate into primary spermatocytes.
115
At what stage of spermatogenesis does meiosis I occur?
The primary spermatocytes proceed through meiosis I to become haploid secondary spermatocytes with two chromatids.
116
What cells are the produced by meiosis II?
Secondary spermatocytes undergo meiosis II to create haploid spermatids.
117
What happens in the process of spermiogenesis?
The spermatids will not divide further but will be transformed into mature spermatozoa by the process called spermiogenesis.
118
What is unusual about the cytoplasm during cell divisions that result in spermatids?
In all the cellular divisions from a progenitor cell to the spermatids, the division of the cytoplasm is never complete. All daughter cells of one progenitor cell will remain connected by cytoplasmic bridges. The mature spermatozoa ultimately become individual cells by shedding their extra cytoplasm along with the bridges connecting them.
119
Why is an undescended testis a problem?
Normal spermatogenesis requires a lower temperature than core body temperature (37¾C), and therefore an undescended (cryptorchid) testis will have impaired spermatogenic potential. Also, cryptorchid testes are much more likely to develop cancers.
120
What cells are responsible for the blood-testis barrier and what are some unique features of these cells?
The Sertoli cells are epithelial cells that contact the basement membrane and that have tight junctions between cytoplasmic processes of adjacent cells. These junctional complexes create the blood-testis barrier. Larger molecules in the blood cannot cross this barrier, so the composition of the fluid in the seminiferous tubule varies from that in the blood. The exchange of nutrients to and metabolites from the developing spermatogenic cells is a function of Sertoli cells, which have no barrier between them and the capillaries deep to the basal lamina.
121
Which cells that are involved in production of sperm are outside of the blood-testis barrier (i.e., are exposed to circulating macromolecules)?
The spermatogonia and early primary spermatocytes reside only in the basal compartment, i.e., in between the basal lamina and the junctional complexes of the Sertoli cells. Prior to the onset of meiosis I a primary spermatocyte must migrate to the luminal (other) side of the junctional complex where the remainder of spermatogenesis takes place.
122
Why is the blood-testis barrier necessary?
The haploid spermatids are genetically different from the host and would be recognized as foreign. However, they are isolated from an immune response by the blood-testis barrier which prevents antigens from the germ cells reaching the systemic circulation and any resulting antibodies in the circulation from reaching the germ cells.
123
What are the steps in spermiogenesis?
This process includes formation of the acrosome, nuclear condensation and elongation, development of the flagellum (a long cilium) and loss of cytoplasm. These flagella projecting into the lumen of the seminiferous tubule. Mitochondria spiral tightly around the proximal end of a flagellum providing an energy source. Before the spermatozoa are released into the lumen, excess cytoplasm is shed as residual bodies.
124
What is the acrosome?
The acrosome is a structure that contains hydrolytic enzymes that permit the sperm to penetrate the corona radiata and zona pellucida of the ovum prior to fertilization.
125
What happens to residual bodies?
Residual bodies and any spermatogenic cell that fails to differentiate completely are phagocytosed by the Sertoli cells.
126
What are the cells that produce androgens, and where are they located?
Interstitial or Leydig cells are in the loose interstitial tissue between the seminiferous tubules. These cells synthesize testosterone.
127
What are the factors that influence production of androgens in the testis?
Testosterone is produced by the interstitial cells under the influence of luteinizing hormone (LH) from gonadotrophs in the adenohypophysis.
128
What are the functions of testosterone?
Testosterone is needed for the development and maintenance of spermatogenesis, secondary male sexual characteristics, accessory sex gland secretion and genital ducts.
129
What is the hormonal control of Sertoli cells?
Follicle stimulating hormone (FSH), also from the same pituitary gonadotrophs, stimulates Sertoli cells to synthesize and secrete androgen-binding protein (ABP). This helps to concentrate testosterone in the luminal compartment of the seminiferous tubule where it is essential for normal spermatogenesis.
130
What are the ducts that convey sperm from the seminiferous tubules to the epididymis and what is their lining?
Leaving the seminiferous tubules, spermatozoa will pass through the tubuli recti (lined with simple cuboidal epithelium) and then through the rete testis (also simple cuboidal). They then pass through the efferent ductules (partially lined ciliated epithelium to help propel the still immotile sperm) and into the epididymis.
131
What is the structure of the epithelium of the epididymis?
The epididymis is lined by a pseudostratified columnar epithelium with long stereocilia.
132
What essential role is played by the epididymis?
The epididymis resorbs a large amount of fluid and stores the sperm until they are released. However, their most important function is that spermatozoa develop their motility during their progression through the epididymis. Without a sufficient amount of time in the epididymis, sperm would not be capable of fertilization. The precise mechanisms for this are not known.
133
What is the structure of the vas (ductus) deferens?
The vas deferens has the same epithelium as the epididymis but has a much thicker muscular wall. Its dilated distal end, located on the posterior surface of the urinary bladder, is called the ampulla and joins with the exit of the seminal vesicle to form the ejaculatory duct, which travels through the prostate gland to empty into the prostatic urethra.
134
How does emission take place?
Emission results from activation of the sympathetic nervous system, which causes peristaltic contraction of the smooth muscle in the wall of the epididymis and vas deferens.
135
What is the structure of the lining of the urethra?
The urethra has prostatic, membranous and penile portions. The epithelium in the penile portion is predominately stratified columnar transitioning to stratified squamous in its distal portion. Mucus secreting urethral glands (of Littré) are present throughout the penile urethra.
136
What is the structure of the seminal vesicles?
The seminal vesicles have a convoluted glandular mucosa covered by a pseudostratified, non-ciliated epithelium that is secretory. The stroma of the seminal vesicles contains an abundance of smooth muscle whose contraction impels the seminal fluid into the ejaculatory duct during emission.
137
What do the seminal vesicles do?
The epithelium secretes a fructose-rich secretion, which is a source of energy for spermatozoa. It does NOT store spermatozoa despite the implications of its name.
138
What is the structure of the prostate gland?
The prostate consists of glandular tissue surrounded by a fibromuscular stroma. The glands are lined by tall columnar or pseudostratfied epithelium. These glands add secretions to the semen. In older men the glands often contain prostatic concretions (corpora amylacea) within the glandular lumens.
139
What is the significance of different zones of the prostate?
There are 3 concentric zones of the prostate. Zone 1 is a central zone surrounding the prostatic urethra. This is the major site of benign prostatic hyperplasia, which often results in constriction of the urethra early in its course. Zone 2 is a transition zone that surrounds the central zone and the ejaculatory ducts. Zone 3 is a peripheral zone, which comprises the majority of the prostate. This is the area where most prostate cancers occur. Therefore, urinary obstruction is usually a late sign of prostate cancer (if it happens at all). On the other hand, this makes prostate cancer more detectable by rectal examination.
140
What are the bulbourethral glands and where are they located?
The bulbourethral (Cowper's) glands lie superior (deep) to the perineal membrane. Their cuboidal epithelium secretes a clear mucus through ducts into the proximal penile urethra inferior to the perineal membrane.
141
What is the structure of the erectile tissues of the penis?
The erectile tissue is made up of a network of endothelial-lined vascular sinuses supported by a network of fibromuscular trabeculae. The engorgement of these sinuses by arterial blood results in erection. The three cylinders of erectile tissue are surrounded by a tunica albuginea. This fibrous sheath is much thicker and more rigid over the corpora cavernosa than over the corpus spongiosum. The glans penis is the distal portion of the corpus spongiosum and has a similarly thin connective tissue capsule.
142
What is the significance of the different connective tissue capsule around the corpus spongiosum and corpora cavernosa?
The thick tunica albuginia around the corpora cavernosa compress venous return and result in a much more rigid structure. The corpus spongiosum, containing the penile (spongy) urethra, does not become as rigid, permitting ejaculation.
