Characteristics of epithelium Many cells with little intercellular substances
Shows polarity-nucleus position and shape, and special locations of organelles and inclusions
Rest on a basement membrane
Functions Form a selective barrier
Classification of covering epithelium
A. Cell shape
B. Number of layers
Simple --- cells in a single layer
Stratified --- cells in two or more layers
Very flattened cells presenting a minimal barrier to the passage of material, e.g. oxygen, through them.
Cytoplasm is very hard to see with LM.
The very similar endothelium and mesothelium, line blood and lymph vessels, and serous cavities, respectively.
Cell height and width are equal
Cell height exceeds width
Cells have three surfaces and sealed at the top of their sides by encircling junctional complexes.
Cells have three surfaces: free/luminal, lateral and basal; each may have membrane specializations, e.g. cilia at free, desmosomes at lateral, and infoldings at basal surfaces.
Pseudostratified columnar --- ciliated; non ciliated
Nuclei lie at different levels suggesting stratified, but all cells are in contact with the basement membrane.
Two or more cell types are present: short basal, tall columnar
Many cells, thick.
Basal most cells are cuboidal or columnar and divide.
Cells above the base become polyhedral and are held on this protective epithelium
Underside of the epithelium is indented by vascular papillae of connective tissue, except in the cornea.
Keratinized stratified squamous
Similar in its basal and middle layers to (5), but the uppermost epithelium has granular cells concerned with forming special, dead cells solidly packed together as a surface keratin layer for greater protection.
Surface cells are cuboidal or columnar in shape, basal most cells are low columnar, and between them are polyhedral cells.
Several cells, thick, the surface cells vary from cuboidal in the relaxed condition to squamous in the distended condition.
Basal layer are cuboidal or low columnar, intermediate layers are polyhedral. Cells of the superficial layer are often binucleate.
Cell adhesion in the epithelial cells’membrane Tight or occluding junction - outer parts of two cells’ membranes are fused together thereby occluding the intercellular cleft.
Metarterioles: with a discontinuous smooth muscle layer
b. Functions: blood pressure & blood flow regulation, and thermoregulation in particular areas.
1) Arterioles (Peripheral resistance vessels)
Diameter < 0.5 mm (including all 3 layers)
1-2 concentric smooth muscle layers in media, thin adventitia
2) Muscular arteries
a. Small arteries d < 1mm (Peripheral resistance vessels)
b. Medium - sized arteries (Distributing Arteries)
Prominent internal elastic lamina, 3-40 concentric smooth muscle layers in media, external elastic lamina usually visible, adventitia equal in thickness to media
3) Elastic Arteries (Conducting Arteries) yellowish color
Relatively thick intima, 40-70 elastic laminae in media, thin adventitia
4) Specialized arteries and age changes in arteries:
a. Carotid bodies & aortic bodies: chemoreceptors, sensing O2 and CO2 tension & pH.
b. Carotid sinuses: baroreceptors, sensing blood pressure.
(3) Veins (Capacitance vessels)
Comparing with their corresponding arteries, veins have valves and squashed, larger lumen, thinner wall, and poorly demarcated layers.
1) Venules diameter < 1mm
pericytes in postcapillary venules, discontinuous or no smooth muscle in media
2) Small to medium-sized veins diameter: 1-9mm
2-4 1ayers of smooth muscle cells in media, intermixed with fibroelastic C.T., thicker adventitia with or without some longitudinal arranged smooth muscle cells. One - way valves in veins > 2mm diameter
Venous valves: paired, semilunar folds of the intima
3) Large veins
relatively thin media, thickest adventitia with many longitudinal bundles of smooth muscles.
Endothelial cells + basal lamina
Subendocardial layer Branches of Purkinje fibers in it
c. Epicardium (Visceral pericardium): CT + mesothelium
2) Fibrous skeleton (cardiac skeleton)
Including annuli fibrosi, the trigona fibrosa & septum membranaceum.
A central core of dense C.T., lined on both sides by endothelial layers
4) Impulse Conducting System
a. Sinoatrial (SA) node: pacemaker, in subepicardial layer
b. Atrioventricular node (AV), in subendocardial layer
c. AV Bundle of His, in subendocardial layer
Purkinje cell: specialized cardiac muscle cells, one or two nuclei, paler cytoplasm; clear (glycogen storage) area forms “halo” around nuclei, reduced number of myofibrils.
B. Lymphatic Vascular System
1. Lymphatic capillaries
Blind ended vessels, endothelial cells have no fenestrate, no tight junction, and little or no basal lamina.
EM: lipid droplets, Mit. (tubular & vesicular cristae), sER
2. Distribution of the endocrine cells
dispersed endocrine cells
3. Characteristics of endocrine gland
cells arrange in cords, clumps or follicles
highly vascularized by fenestrated capillaries (sinusoids)
II. Pituitary gland (hypophysis) Embryogenesis
adenohypophysis: oral ectoderm (Rathke’s pouch)
neurohypophysis: neural ectoderm (diencephalon)
pars distalis anterior lobe
adenohypophysis pars tuberalis
neurohypophysis infundibular stem
1) Pars distalis
arranged in cords
follicle stimulating hormone (FSH)
luteinizing hormone (LH)
(2) Chromophobes 50%
2) Pars intermedia
follicles & cords
chromophobes & basophils
3) Pars tuberalis
abundant longitudinal blood vessels
cell arranged in cords
basophils: may secrete gonadotropins
1) Unmyelinated nerve fibers
2) Pituicytes: neuroglial cells
3) fenestrated capillaries
4) Herring bodies
5. Blood supply
hypophyseal portal system
superior hypophyseal A.
primary capillary plexus
secondary capillary plexus
inferior hypophyseal A.
6. Hypothalamo - hypophyseal system
the hypothalamus and adenohypophysis
neuroendocrine cells in tuberal nuclei, etc (releasing hormones, RH & releasing inhibiting hormones, RIH the portal system the endocrine cells in pars distalis target cells in other organs
the hypothalamus and neurohypophysis
neuroendocrine cells in supraoptic and paraventricular nuclei
a. Spermatogonia: located in basal compartment, mitosis
Dark type A spermatogonia: heterochromatin
Pale type A spermatogonia: euchromatin
Type B spermatogonia:
b. Primary spermatocyte: the largest male germ cells, having chromosome within their nuclei.
c. Secondary spermatocytes: short-lived cells
Spermiogenesis: round spermatids elongated spermatids, through shedding of much of their cytoplasm, rearrangement of their organelles, and formation of flagella
Nucleus becomes condensed and elongated sperm head
Golgi apparatus acrosome (acrosomal cap) (a specialized lysosome)
proacrosomal granules acrosomal granule within a acrosome vesicle
Mitochondria mitochondrial sheath
Microtubuli manchette (caudal tube)
Residual bodies are shed, and phagocytosed by Sertoli cell
e. Spermatozoon morphologically mature
Tail: middle piece, principal piece, end piece
Clonal nature of the germ cells
Cytoplasmic bridges & Syncytium of germ cells
The cycle of seminiferous epithelium
The waves of seminiferous epithelium
2) Sertoli cells
LM: tall columnar cell; a large, pale, oval or irregular shaped nucleus with a prominent nucleolus; invisible lateral cellular limits.
EM: lateral and apical cell membrane & nucleus with infoldings; many organelles; tight junctions & gap junctions.
Support, protection and nutrition of developing germ cells.
Phagocytosis of residual bodies.
Secretion. e.g.: androgen-binding protein (ABP), anti-müillerian hormone & inhibin, and a fructose - rich medium.
Formation of blood-testis barrier.
Regulation the release of spermatozoa
3. Interstitial tissue
(1) Interstitial cell (Leydig cell):
LM: always in clusters; large, polyhedral cells, acidophilic cytoplasm, central located nucleus.
EM: typical steroid-producing cells, containing large amounts of sER, mitochondria with tubular cristae, and numerous of lipid droplets.
2) Function: secretion of testosterone.
(2) Others: including C.T., nerve, blood & lymphatic vessels.
4. intratesticular genital ducts:
(1) tubuli recti (straight tubules):
Lined by Sertoli cells in proximal half and simple cuboidal epithelium in distal half, supported by loose C.T.
(2) Rete testis:
A system of labyrinthine spaces housed within the mediastinum testis, lined by simple low cuboidal epithelium, supported by vascular C.T.
(3) Ductuli efferentes:
Undulated lumen lined by pseudostratified columnar E., supported by loose C.T., forming the head of the epididymis.
III. Extratesticular genital ducts
1. Ductus epididymidis
Forming the body and tail of the epididymis
Lined by pseudostratified columnar epithelium of uniform height, composed of basal cells and tall principal cells, the latter have many long stereocilia and are actively reabsorptive. Epithelium is supported by loose C.T. and abundant circularly arranged smooth muscles.
2. Ductus deferens (Vas deferens)
A narrow lumen and a thick-walled tube lined by pseudostratified columnar epithelium with stereocilia, and surrounded by 3 layers of smooth muscle: inner and outer longitudinal layers and middle circular layer.
Spermatic cord: passes through the inguinal canal, including arteries, veins and ductus deferens.
Countercurrent heat-exchange system
3. Ejaculatory duct
Lined by a simple columnar epithelium, and supported by loose C.T.
(1) Prostatic urethra Transitional E.
(2) Membranous urethra Pseudostratified columnar E.
(3) Spongious part (bulbous part and pendulous part)
Pseudostratified columnar E.
Glands of Littre
IV. Accessory sex glands
1. Seminal vesicles
Highly coiled tubuli, lined by pseudostratified columnar epithelium, and supported by fibroelastic C.T. and smooth muscles, producing fructose - rich seminal fluid that is energy source for sperm motility.
2. Prostate gland
An collection of branched tubuloalveolar glands, the epithelium ranges from simple cuboidal - columnar to pseudostratified columnar depending on the man's hormonal states, and the glands are embedded within a fibromuscular stroma. Three groups of glands concentrically arranged around the urethra:
(1) Mucosal glands (central zone)
(2) Submucosal glands (transition zone)
(3) Main glands (peripheral zone)
Prostatic concretions (corpora amylacea)
3. Bulbourethral glands
Tubuloalveolar, mucus-secreting glands, lined by a simple cuboidal or columnar epithelium.
Each of three columns of erectile tissue, which is encircled by tunica albuginea, has large venous sinuses separated by trabeculae.
(1) Corpora cavernosa of the penis: Paired, located dorsally.
Helicine arteries & Intimal cushion
(2) Corpus cavernosum of the urethra (corpus spongiosum): ventrally located, containing penile urethra.
(2) Copulation organ
Penile erection: a hemodynamic event
The Female Reproductive System
1. Oogenesis: miosis of oocyte
oogonia primary oocytes ① secondary oocytes ② ovum
polar body polar body
stopped in prophase of meiosis I, completed before ovulation
stopped in metaphase of meiosis II, completed when fertilization taken place
2. General structures
1) Ovarian surface epithelium:
simple squamous/cuboidal epithelium
2) Tunica albuginea
stroma: C.T., stromal cells, smooth muscle
gamete - producing structures & derivatives
hilus cells: secrete androgen
3. Structures in cortex
1) Follicular growth
follicle: an oocyte + follicular cells
basement membrane surround the follicles
(1) Primordial follicles
primary oocyte + a single layer of flattened follicular cells