Histology 🔬 Flashcards
1
Q
what is the definition of endocrine gands?
A
ductless glands secreting hormones→blood stream→target organ.
2
Q
what are the major encocrine glands in the body?
A
- Pituitary gland
- Pineal body
- Thyroid & parathyroid glands
- Suprarenal gland
3
Q
what are the master organs of the endocrine system?
A
The pituitary gland and the hypothalamus are called the master organs of the endocrine system.
4
Q
What is the hypothalamus?
A
The portion of the brain to which the pituitary gland is attached.
5
Q
what is the median eminence?
A
a structure at the base of the hypothalamus which acts as a functional link between the hypothalamus and the anterior pituitary gland.
6
Q
what is the size of the pituitary gland?
A
pea-sized, compound endocrine gland.
7
Q
what is the site of the pituitary gland?
A
at the base of the brain, where it lies in a depression in the sphenoid bone called the sell turcica.
8
Q
what is the infindibulum?
A
a short stalk connecting the pituitary gland to the
hypothalamus.
9
Q
what forms the pituitary gland?
A
* Anterior lobe (adenohypophysis):
a- Pars distalis.
b- Pars tuberalis.
c- Pars intermedia.
* Posterior lobe (neurohypophysis):
a- Pars nervosa.
b- Infundibulum (infundibular stalk, pituitary stalk).
10
Q
compare between the anterior lobe (adenohypophysis) & the posterior lobe (neurohypophysis) accoding to staining, structure & parts
A
11
Q
what is the histological structure of pars distalis?
A
stroma & parenchyma
12
Q
stroma of pars distalis
A
a- Dense fibrous capsule.
b- Trabeculae extending from the capsule.
c- Reticular fibres surround the cords of cells
13
Q
parenchyma of pars distalis
A
- Irregular anastomosing cords of cells.
- Surrounded with fenestrated capillaries.
- The cells are classified on the basis of their affinity or lack of affinity for dyes of routine staining (haematoxylin & eosin)
14
Q
what are the cells in the parenchyma of pars distalis?
A
15
Q
compare between acidophilic cells (alpha cells) and basophilic cells of pars distalis
A
16
Q
what is the EM of pars distalis?
A
The cells of pars distalis reveal rER, mitochondria, a well developed Golgi apparatus & electron dense granules of variable size.
17
Q
what is the site of Somatotrophs (somatotropic cells)?
A
They occur in groups along the blood sinusoidal capillaries.
18
Q
what is the LM of Somatotrophs (somatotropic cells)?
A
- Shape: rounded cells.
- Stain:
H & E: stain intensely with eosin
PAS: -ve.
19
Q
what is the EM of Somatotrophs (somatotropic cells)?
A
- rER, mitochondria, Golgi apparatus.
- Granules: numerous, spherical & electron dense (300-350 nm).
20
Q
what is the function of Somatotrophs (somatotropic cells)?
A
secrete growth hormone.
21
Q
what is the LM of Mammotrophs (prolactin cells) (Lactotroph cells)?
A
Site: They are distributed singly in the interior of the cell cords.
Shape: fusiform.
Stain: H & E: stain intensely with eosin, PAS: -ve.
22
Q
what is the EM of Mammotrophs (prolactin cells)?
A
- rER, mitochondria, Golgi apparatus.
- Granules: numerous & electron dense (200 nm).
23
Q
what happens to Mammotrophs (prolactin cells) during pregnancy?
A
- The cells hypertrophy under the stimulating effect of estrogen.
- Their granules become larger and irregular (600 nm) & they are called pregnancy cells.
24
Q
what is the function of Mammotrophs (prolactin cells)?
A
secrete prolactin hormone.
25
what is the LM of Thyrotrophs?
* Shape: polygonal.
* Stain:
H & E: stain poorly.
PAS: +ve.
26
what is the EM of Thyrotrophs?
- rER, mitochondria, Golgi apparatus.
- **Granules:** small (140-160 nm).
27
what is the function of Thyrotrophs?
secrete thyrotrophic hormone (thyroid stimulating hormone) TSH.
28
what is the LM of Corticotrophs?
* Shape: oval or round.
* Stain:
H & E: stain poorly.
PAS: +ve.
29
what is the EM of Corticotrophs?
- rER, mitochondria, Golgi apparatus.
- **Granules:** 100-200 nm.
30
what is the function of Corticotrophs?
secrete synthesise a pro-hormone, by cleavage, they produce:
* ACTH which controls the function of suprarenal cortex.
* Melanocyte stimulating hormone & endorphin.
31
what is the LM of Gonadotrophs or (FSH-LH cells)?
* Shape: rounded.
* Stain:
H & E: stain poorly.
PAS: +ve.
32
what is the EM of Gonadotrophs or (FSH-LH cells)?
- rER, mitochondria, Golgi apparatus.
- **Granules:** variable in size & electron density (200-400 nm).
33
what is the function of Gonadotrophs or (FSH-LH cells)?
secrete follicle stimulating hormone (FSH) & luteinizing hormone (LH).
34
what is the LM of Chromophobic Cells?
* They occur in groups.
* Shape: rounded.
* Stain: lack affinity to stains.
35
what is the EM of Chromophobic Cells?
- Organelles: few.
- Granules: no or few.
36
what is the function of Chromophobic Cells?
- reserve cells capable of differentiation into either acidophils or basophils.
- exhausted glandular cells.
37
what does pars tuberalis form?
- It forms a collar surrounding the infundibulum of the neurohypophysis.
38
vascularity of pars tuberalis
It is a highly vascular region containing veins of the hypothalamo-hypophyseal system.
39
what do the cells of pars tuberalis secrete?
Most of the cells of the pars tuberalis secrete gonadotropins (FSH & LH) and are arranged in cords alongside the blood vessels.
40
what is pars intermedia?
It is a rudimentary region in human.
41
what cells does pars intermedia contain?
- It contains pale basophilic cells that contain small secretory granules.
- The cells often surround follicles filled with colorless colloid.
42
what is the function of pars intermedia?
It plays a role in the production of melanocyte-stimulating hormone (MSH).
43
# **"2 components, 2 cells & 2 fibers"**
what is the histological structure of pars nervosa?
**1- Nerve fibres:**
- **Unmyelinated axons** of hypothalamic neurosecretory neurons of the paraventricular and supra-optic nuclei.
- The axons end close to the fenestrated capillaries
**2- Herring bodies:**
- **Basophilic masses** formed of **accumulation of neurosecretion** in the terminal ends of the nerve fibres.
**3- Fenestrated capillaries**.
**4- Pituicytes:**
- Are **branched neuroglial cells**.
- Form about **25% of the pars nervosa volume**.
**5- Neuroglia cells**.
**6- Reticular fibres:** around the capillaries.
N.B: Pars nervosa **does not contain secretory cells**.
44
what are the functions of pars nervosa?
- It is the **reservoir for the neurosecretion** (oxytocin & vasopressin or antidiuretic hormone), which is formed by the neurons of the **supraoptic and paraventricular nuclei of the hypothalamus**.
45
what happens to the secretory granules of pars nervosa?
- The secretory granules descend along the axons of the pituitary stalk and accumulate in the terminal bulbs nearby the fenestrated capillaries as Herring bodies.
- The secretory granules are absorbed to the circulation.
46
what is the Pineal body (Epiphysis cerebri)?
A small Cone shaped median endocrine gland
47
what is the site of the Pineal body (Epiphysis cerebri)?
- located at the **posterior wall of the third ventricle near the center of the brain**.
- It is **attached to the roof of 3rd ventricle** by a short stalk.
48
what is the histlogical structure of Pineal body (Epiphysis cerebri)?
**Stroma:**
A- Capsule: CT covered with **pia mater**.
B- Trabeculae: Septa between **poorly defined lobules** carrying blood vessels.
**The parenchyma:** (consists of)
A-Pinealocytes
B-Astrocytes
C-Calcified concretions (Brain sand)
49
what is the LM of Pinealocytes?
**Shape:** irregular.
**Cytoplasm:** pale basophilic
**Nucleus:** large, ovoid or polymorphic with one or two prominent nucleoli.
50
what are the types of processes of Pinealocytes?
- **Short and thin processes** which end on the **adjacent pinealocytes.**
- **Longer and thinner processes** which terminate on the **blood vessels.**
51
what is the EM of Pinealocytes?
sER, rER, free ribosomes, mitochondria, microtubules and electron dense granules.
52
what is the function of Pinealocytes?
they secrete melatonin.
53
Circadian changes of melatonin secretion
- increase the plasma level of melatonin during darkness and its decrease during light, **play an important role in regulating daily body rhythms as sleep**.
54
what is the shape of astrocytes?
- Elongated nuclei that stain more heavily than pinealocytes.
- Long cytoplasmic processes that contain a large number of intermediate filaments.
55
what is Calcified concretions (corpora arenacea, brain sand)?
- It is a calcified concretion containing hydroxy apatite.
56
what is the site of Calcified concretions?
They are generally present in the human pineal body.
57
Relation of brain sand to age
They tend to increase in number with age.
58
where does brain sand appear?
- They appear as concentric zones of concretions within the organ.
- They are median intracranial landmark visible in X-ray.
59
what are the characters of thyroid gland?
- It is highly vascular.
- It is the only endocrine gland whose secretory product is stored in great quantity extra-cellularly (Colloid)
60
what is the shape of Thyroid gland?
butterfly shape
61
what is the structure of Thyroid gland?
Consists of two lobes, connected by an isthmus.
62
what is the site of Thyroid gland?
Located in front of the Trachea below the Adam's apple
63
what is the histological structure of Thyroid gland?
**Stroma:** Rich in blood capillaries, lymphatics and nerves
**Parenchyma:** (Thyroid Follicles & interfollicular cells)
64
stroma of Thyroid gland
**Capsule:**
- False capsule: an outer fascial sheath
- True Capsule: an inner delicate CT capsule
**Trabeculae:**
- divide the gland into incomplete lobules.
**Reticular fibers:**
- silver stain
65
parenchyma of Thyroid gland
Thyroid follicle: structural and functional unit of the gland.
**Shape:** Spherical or oval
**Number:** 30 million in the gland.
**Structure:** lined by two type of cells:
1. Follicular cells (98%)
2. C-cells (2%).
**Lumen:** contains gelatinous substance colloid ( acidophilic material)
66
what is the morphologic appearence of the Thyroid gland follicles?
The morphologic appearance of the follicles varies according to the region of the gland and its functional activity (In the same gland larger follicles full of colloid and have low cuboidal epithelium are found beside smaller follicles which are lined with columnar cells).
67
what is the percentage of Follicular Cells?
represent 98% of the lining epithelium.
68
LM of Follicular Cells
**Shape:** cubical secretory cells
**Nucleus:** Central rounded
**Cytoplasm:** Basophilic
69
EM of Follicular Cells
1. Mitochondria
2. Well developed rER
3. Supra-nuclearGolgi
4. Lysosomes
5. Fine droplet of colloid
6. The free border reveals short microvilli projecting in the lumen.
7. The cells are adherent to each other by tight junctional complexes.
70
what is the function of Follicular Cells?
Synthesis and release of thyroid hormones
71
steps of synthesis of T3&T4
1. Synthesis of glycoprotein containing tyrosine A.A. by rER, Golgi and discharge it in the lumen by exocytosis.
2. Uptake of iodide by a process of active transport (iodine pump via basal cell membrane of the follicular cell).
**This Step can be inhibited by perchlorate & thiocyanate drugs.**
3. Activation of iodide by peroxidase oxidation.
4. Iodination of tyrosine residues to thyroglobulin takes place in the colloid in contact with the cell membrane at the apical region to form Mono-iodotyrosine ( MIT) & Di-iodotyrosine (DIT )
**MIT + DIT → tri-iodothyronine (T3)**
**DIT + DIT → thyroxine (T4)**
72
steps of liberation of T3&T4
1. When the gland is stimulated by TSH, the follicular cells take up the colloid by sending pseudopodia to phagocytose droplets of colloid.
2. By the action of the hydrolytic enzymes present in lysosomes, the thyroid hormones (T3 & T4) are released to capillaries surrounding the follicles.
73
what is the definition of colloid?
It is an inactive precursor of T3 and T4.
74
what forms colloid?
It is made up of a glycoprotein called thyroglobulin, made by the epithelial cells, which is bound to iodine
75
staining of colloid
a homogenous acidophilic. It stains intensely with PAS and is eosinophilic with H & E.
76
what are the functions of thyroid hormones?
1. Stimulate metabolism of protein, Lipid &CHO
2. Stimulate erythropoiesis
3. Stimulate growth of body skeleton & organs
4. Increase Sympathetic activity & ↑ BMR
77
what are the effects of TSH?
1. Enlarges the follicular cells
2. increases the synthesis and secretion of glycoprotein.
3. Enhances iodine trapping
4. Enhances iodination of the colloid.
5. Increases Breakdown of thyroglobulin and liberation of hormones
78
what is the percentage of Parafollicular cells (C cells & Clear cells)?
2%
79
LM of Parafollicular cells (C cells & Clear cells)
**Site:** Resting on basal membrane but they do not reach the lumen of the follicle.
**Size:** Larger than the follicular cells.
**Shape:** Rounded or oval
**Nucleus:** Rounded
**Cytoplasm:** Paler than the follicular cells
80
EM of Parafollicular cells (C cells & Clear cells)
- Small rER
- Long Mitochondria
- Golgi Apparatus.
- Abundant spherical secretory granules (100-200 nm).
81
what is the function of Parafollicular cells (C cells & Clear cells)?
- Secretion of Calcitonin hormone which lowers blood calcium by suppressing osteoclast activity in the bones, decrease intestinal absorption of ca+ and increasing the amount of calcium excreted in the urine.
82
what are Inter follicular cells? and what do they consist of?
- Masses of cells present in-between the follicles, They represent tangentially cut follicles.
- They consist of follicular cells and para-follicular
83
what are the histological characters of Hyper-thyrodism?
- The gland is Hyperactive.
- Depletion of the colloid.
- Follicular cells are tall columnar with basal oval nuclei, e.g., Graves' disease (autoimmune thyrotoxicosis).
84
what are the histological characters of Hypo-thyrodism?
- The gland is Hypoactive.
- The gland is distended with colloid.
- Follicular cells are flattened.
- If in children →Cretinism, If in adults → Myxedema
85
what are thyroid gland disorders?
Hyperthyroidism & Hypothrodism
86
Different levels of thyroid activity and morphology of secretory cells
87
what are the results of iodine deficiency in diet?
- Hinders synthesis of thyroid hormones (↓ Thyroxin)
- Increased TSH secretion by feedback mechanism on Pituitary gland
- Hypertrophy and hyperplasia of thyroid follicles
- Thyroid gland enlargement Known as Goiter
88
what is the number of Parathyroid glands?
4 small glands
89
what is the site of Parathyroid glands?
Posterior surface of thyroid gland
90
what is the size of Parathyroid glands?
3-6mm
91
what is the histological structure of Parathyroid glands?
stroma & parenchyma
92
stroma of Parathyroid glands
**Capsule:** surrounds the gland and separate it from thyroid gland.
**Trabeculae:** divide the gland into incomplete lobules.
**Reticular fibers**
93
parenchyma of Parathyroid glands
- anastomosing cords of cells separated by blood capillaries
1. Chief cells.
2. Oxyphil cells.
94
compare between chief cells and oxyphil cells according to LM,EM & functions
95
what are the cytological characters of transitional cells of parathyroid glands?
They have cytological characteristics, intermediate between chief and Oxyphil cells.
96
what are parathyroid disorders?
hyper & hypo function
97
what does hyper-function of parathyroid glands lead to?
- Leads to increased calcium level and decreased phosphorus level
- Calcium deposition in several organs as kidney and arteries
- Bone matrix is decalcified leading to easy fractures, a condition known as Osteitis fibrosa cystica
98
what does hypo-function or removal of parathyroid glands lead to?
leads to Tetany and death due to decreased calcium level
99
histological structure of adrenal gland
stroma & parenchyma
100
stroma of adrenal gland
**Capsule:** Dense fibrous C.T
**Trabeculae:**
- From the deep surface of capsule
- Extend in the cortex.
- Carry blood vessels.
**Reticular fibers:**
- Support the sinusoidal capillaries and the parenchymal cells.
101
parenchyma of adrenal gland
cortex and medulla
102
what are the zones of Suprarenal Cortex?
A. Zona Glomerulosa
B. Zona Fasciculata
C. Zona Reticularis
103
what is the structure of Zona glomerulosa?
- It is a **relatively narrow zone** under the capsule.
- The cells are arranged into **round and oval groups (glomeruli)**.
- A rich network of capillaries surrounds the glomeruli.
104
LM of Zona glomerulosa
Columnar cells with **spherical deeply stained nuclei** and **few lipid droplets**.
105
EM of Zona glomerulosa
- Well-developed **sER**
- Golgi apparatus
- Mitochondria.
106
what are the functions of Zona glomerulosa?
Secrete mineralo-corticoid (aldosterone).
107
what is the structure of Zona Fasciculata?
- It is the **broadest zone**, composed of straight parallel cords of cells.
**The cords:**
- Usually one or two cells in width.
- Surrounded by a longitudinally arranged fenestrated sinusoidal capillaries.
108
LM of Zona Fasciculata
- **Shape:** polyhedral
- **Nucleus:** large vesicular nuclei (binucleated)
- **Cytoplasm:** vacuolated and has a spongy appearance **(spongiocytes)**
109
EM of Zona Fasciculata
numerous mitochondria with **tubular cristae**.
110
what are the functions of Zona Fasciculata?
Secrete gluco-corticoids (Cortisol and hydro cortisone).
111
what is the structure of Zona reticularis?
- It is a **relatively thin zone**.
- It is composed of **branching and anastomosing cords** of cells separated by fenestrated blood sinusoidal capillaries.
112
LM of Zona reticularis
- Small, polyhedral with few lipid droplets.
- Some cells are darker (dark cells) as they contain lipofuscin pigment.
113
what are the functions of Zona reticularis?
Secrete sex hormones and small amounts of gluco-corticoids.
114
histological structure of Suprarenal Medulla
115
LM of Chromaffin cells
**Arranged in groups around the blood vessels and fenestrated capillaries.**
**Shape:** polyhedral *"nearly all cells, except those of zona glomerulosa, are polyhedral"*
**Nucleus:** eccentric
**Cytoplasm:** basophilic containing fine granules of adrenaline and nor-adrenaline
116
EM of Chromaffin cells
Mitochondria, free ribosomes, rER , Golgi complex & **granules**.
117
what are the types of Chromaffin cells distinguished according to?
1. The electron density.
2. shape and size of the stored granules.
118
how to identificate suprarenal medulla from suprarenal cortex?
**Chromaffin reaction:** fresh specimens of the suprarenal gland + potassium dichromate ---> the cells of the medulla revealed brown granules. (Positive chromaffin reaction).
119
what is the function of suprarenal medulla (Chromaffin cells)?
Under stress conditions, they secrete adrenaline and noradrenaline directly into the blood causing a rapid generalized sympathetic effect.
120
what is the definition of Islets of Langerhans?
Non capsulated masses of endocrine cells
121
what is the site of Islets of Langerhans?
Scattered in the pancreatic lobules especially at the tail region
122
what is the number of Islets of Langerhans?
About 1⁄4 - 3⁄4 million (in human)
123
what is the structure and staining of Islets of Langerhans?
- They are formed of anastmosing cords of cells separated by fenestrated blood capillaries
- **In H. & E.:** light non capsulated areas surrounded by darker acini
124
what does Differentiation of the islet cells depend on?
- Specific stains
- E/M features
- Immunohistochemical techniques
125
what are the types of islets cells?
126
LM of ganglion cells of islets of langerhans
- Multipolar neurons having irregular outline and central nuclei
- Form small aggregations between islet cells
127
what is the function of ganglion cells of islets of langerhans?
Involved in nervous control of islet cell functions
128
compare between endocrine cells of islets of langerhans
