Endocrine System Flashcards
What are Ductless glands
Pituitary
Thyroid
Parathyroid
Adrenal
Pineal
Endocrine
Hormone released into blood and acts on distant cells
Paracrine
Hormone is diffused locally and acts on neighboring cells
Autocrine
Acts on the cell that is producing it
What are Hormones
Hormones are chemical messengers that are carried via the blood to distant target cells.
What are types of hormones
Hormones include water-soluble proteins/glycoproteins and lipid soluble steroid hormones.
Water-soluble hormones
Act via specific cell-surface receptors, which then activate a second messenger
meaning, they bind with cell membrane receptors and then activate the second messenger
How do Lipid soluble steroid hormones bind to cell membrane
Diffuse across the cell membrane, bind to nuclear receptors, and activate the transcription of DNA.
Meaning, they cross the cell membrane and bind with cytoplasmic or nuclear receptors and then activate DNA Transcription
Major Endocrine Organs
Organs whose sole function is to synthesize and secrete hormones
Pituitary, Thyroid, Adrenal
Endocrine Components within other Organs
Endocrine cells are distributed within organs which also have non-endocrine functions such as:
Islets of langerhans in the pancreas
Leydig cells in the testis
Granulosa and theca cell in the ovary
JG cells in the kidney
Diffuse Endocrine cells
These endocrine cells are distributed individually or in small groups within epithelium of the digestive system
Argentaffin cells
Pituitary gland
A major endocrine organ that is connected with the hypothalamus
Ductless gland
Two subdivisions of the Pituitary gland
Adenohypophysis (anterior pituitary)
Neurohypophysis (posterior pituitary)
Adenohypophysis (anterior pituitary)
pars distalis
pars tuberalis,
and pars intermedia
Neurohypophysis (posterior pituitary)
median eminence,
infundibulum,
and pars nervosa.
Species differences in gross positions of different parts of the pituitary
For humans, the classical division of the pituitary gland into anterior lobe and posterior lobe is true only in humans and to some extent in the bovine and porcine
In equine,felines, canines, the pituitary gland is compressed dorso-ventrally
Development of the Adenohypophysis of the pituitary gland
Develops from an ectodermal derivative of the stomodeum which is called the Rathke’s pouch
Development of the Neurohypophysis of the pituitary gland
Develops from an evagination of the diencephalons
What is the Pars Distalis
Part of the Adenohypophysis(anterior lobe) of the pituitary gland
Cells arranged in irregular cords that lie adjacent to sinusoids
What are the two cell types of the Pars Distalis
Chromophils
Chromophobes
What are Chromophils
Cytoplasm stained cells in the pars distalis:
Acidophils
Basophils
Acidophils
Are PAS -ve
Secrets protein hormones
Somatotroph
Lactotroph/ Mammotroph
Somatotrophs
Makes up 50% of chromophils
Secretes protein hormone GH (Growth Hormone)
Mammotrophs/ Lactotrophs
Makes up 20% of chromophils
Secretes the protein hormone Prolactin
Basophils
PAS +ve
Secretes glycoprotein hormones
Gonadotroph
Corticotroph
Thyrotroph
Thyrotrophs
Makes up 5% of chromophils
Secretes the glycoprotein TSH (Thyroid Stimulating Hormone)
Gonadotrophs
Makes up 5% of chromophils
Secretes the glycoproteins LH ( Luteinizing Hormone) and FSH (Follicle stimulating Hormone)
Corticotrophs
Makes up 20% of chromophils
Secretes the glycoprotein ACTH
Chromophobes
Stem cells for chromophils
Their cytoplasm is unstained
What is Pars Intermedia
Part of the adenohypophysis of the pituitary gland
Contains colloid-containing cysts which represents remnants of the Rathke’s Pouch
What types of cells are in Pars intermedia
Melanotrophs
Corticotrophs
Melanotrophs
Secretes MSH (Melanin Stimulating Hormone)
Clinical significance of Corticotrophs in the Pars Intermedia
These cells can hypertrophy or under go hyperplasia especially i the horse, leading to excessive secretion of ACTH, which in turn, causes excessive secretion of cortisol from the adrenal cortex
LEADS TO CUSHING’S SYNDROME
What is the Pars Nervosa of the pituitary gland
Part of the Neurohypophysis (Posterior lobe).
Contains the unmyelinated axons of neurosecretory cells whose cell bodies located in the supraoptic and paraventricular nuclei of the hypothalamus.
Besides unmyelinated axons, pituicytes (glia-like cells) are present in pars nervosa.
What hormone does the Supraoptic Nuclei secrete
Vasopressin (ADH)
Target site:
What hormone does the Paraventricular Nuclei secrete
Oxytocin
Target site:Mammary Gland, Uterus
Where are the hormones that are secreted by the supraoptic and paraventricular nuclei transported to
Are transported to the distal ends of hypothalamo-hypophyseal axons and is the site where these hormones are stored in accumulations known as Herring bodies.
Hypothalamic hypophyseal portal system
Primary capillary plexus comes off the superior hypophyseal artery, is in the median eminence where stored hypothalamic neurosecretory hormones (releasing and inhibitory) enter the blood; is drained by hypophyseal portal veins, which enter the pars distalis and empty into a secondary capillary plexus that consists of sinusoids surrounding cells of the pars distalis
Hormones of the pars distalis
Somatotropin (GH), prolactin, ACTH, FSH, LH, and TSH.
Hormones of the pars nervosa
Oxytocin, vasopressin (ADH).
Note: these hormones are only stored here but are secreted by SO and PV nuclei of the hypothalamus.
Hormones of the hypothalamus entering the pars distalis
GH-RH, GnRH, CRH, TRH, GH-IH (somatostatin), and PIH (dopamine).
Clinical Considerations of the Pituitary Gland
Pituitary tumors are not uncommon, are treated by surgical removal.
Thyroid Gland
A major endocrine organ that consists of two lobes connected by the isthmus
Development of the Thyroid Gland
Develop from the endoderm between the first and second pharyngeal pouches
What is the Thyroid Gland made/ consist of
Consist of follicles, spherical structures filled with colloid (iodinated thyroglobulin glycoproteins, precursor of thyroxin),
The follicle of the Thyroid is lined by what type of epithelium
Simple Cuboidal Epithelium
(lined by follicular cells (98%) and parafollicular cells (2%, develop from the ultimobranchial body), and are surrounded by fenestrated capillaries)
What are follicular cells of the thyroid
Cuboidal in shape but become columnar when stimulated by TSH and squamous when inactive.
What are follicular cells involved in
Cells are involved in the synthesis and release of thyroid hormones, T4 and T3, the former is abundant, but the latter is more potent.
Steps involved in the synthesis and release of thyroid hormone:
1) synthesis of thyroglobulin
2) uptake of iodide
3) oxidation of iodide
4) tyrosine iodination
5) resorption of thyroglobulin and release of T4 and T3 into the circulation.
Step 1 of thyroid hormone synthesis: Synthesis of Thyroglobulin
Step 2 of thyroid hormone synthesis: Uptake of iodide
Step 3 of thyroid hormone synthesis:
Step 4 of thyroid hormone synthesis:
Step 5 Step 1 of thyroid hormone synthesis
Physiological effects of T4 and T3
Increase the basal metabolic rate and thus promote heat production, have broad effects on gene expression and induction of protein synthesis.
What are parafollicular cells
Surround follicular cells, found in small clusters between the follicular cells and basal lamina.
What do parafollicular cells secrete
Synthesize and secrete calcitonin (thyrocalcitonin), a polypeptide hormone which is released in response to high blood calcium level (hypercalcemia)
What is the function of Calcitonin
Function is to lower blood calcium level by inhibiting osteoclastic activity.
Clinical significances of the thyroid
1) Graves’ disease
2) Simple goiter
Myxedema and cretinism (hypothyroidism)
Grave’s Disease
Characterized by exophthalmos (exophthalmic goiter), hyperexcitability (nervous symptoms), enlargement of thyroid gland, excessive production of thyroxine, decreased level of TSH.
Caused by the binding of autoimmune IgG antibodies to TSH receptors.
Simple Goiter
Enlargement of the thyroid gland caused by insufficient iodine in the diet, treated by dietary iodine.
Myxedema and cretinism (hypothyroidism).
Where is the Parathyroid Located
Located on the caudal surface of the thyroid gland, as well as embedded in its capsule; develop from ventral diverticula of third and fourth pharyngeal pouches.
What are the two types of cells in the Parathyroid
Chief Cells
Oxyphil
Chief Cells
Present in all species and numerous
What do Chief Cell secrete
Secrete parathyroid hormone
Function of Parathyroid hormone
Raise blood calcium levels by stimulating osteoclastic activity and by increasing reabsorption of calcium and decreasing reabsorption of phosphates at the proximal tubules of the kidney. Parathyroid hormone is antagonistic to calcitonin hormone.
Oxyphil compared to Chief cells
Relatively larger in size, few, present in horse and large ruminants but rare in other species.
Clinical significance of parathyroid
Hyperparathyroidism
Where is the Adrenal Gland
Located at the anterior pole of each kidney
The development of the Adrenal gland
Derived from two embryonic sources: cortex from the mesoderm and medulla from the ectodermal neural crest cells.
Where is the medulla of the Adrenal Gland present in animals
The medulla is present as a separate organ in lower vertebrates, randomly mixed with cortical tissue in birds, and centrally located in mammals.
How is the Adrenal cortex divided for mammals
Cortex in mammals is divided into three regions:
zona glomerulosa (ZG)
zona fasciculata (ZF)
zona reticularis (ZR).
How are the parenchymal cells of the Adrenal Gland arranged
Parenchymal cells are arranged in longitudinal cords/columns, which are surrounded by longitudinally oriented sinusoidal capillaries
What do the parenchymal cells of the adrenal gland secrete
All cells secrete steroid hormones.
How are adrenal cells characterized
Hence, these cells are characterized by mitochondria with tubular cristae, abundant SER, and lipid droplets.
How are steroid hormones different from protein/glycoprotein hormones
Steroid hormones are not stored, but are secreted as soon as they are synthesized
Protein/glycoprotein hormones are stored intracellularly before being secreted into the blood
Where is the Zona glomerulosa (ZG) of the Adrenal Gland located
Is located just beneath the capsule
How the cells in the Zona glomerulosa (ZG) arranged in horses, carnivores, and pigs
Cells are arranged in the form of arches
How the cells in the Zona glomerulosa (ZG) arranged in ruminants and man
Cells are arranged in the form of clusters
What do the cells in Zona glomerulosa (ZG) secrete
Secretes mineralocorticoids (aldosterone), regulates electrolyte balance.
How are the hormones in the Zona glomerulosa (ZG) stimulated
Angiotensin II (mainly) and ACTH (limited control).
What conditions stimulate aldosterone secretion directly
Hypovolemia, hyponatremia, and/or hyperkalemia can stimulate aldosterone secretion directly and/or via the renin-angiotensin system
A tumor of corticotrophs will have a minimal effect on aldosterone secretion; explain why?
What is the Zona Fasciculata (ZF)
Is the largest region of the adrenal cortex
Constitutes up to 80% of its volume, can be divided into outer (cells more vacuolated and are referred to as spongiocytes) and inner fasciculata; secretes glucocorticoids (cortisol and corticosterone);
How is the Zona Fasciculata Divided
Can be divided into outer (cells more vacuolated and are referred to as spongiocytes)
and inner fasciculata
What do the cells in the Zona Fasciculata secrete
Secretes glucocorticoids (cortisol and corticosterone)
Function of Glucocorticoids
secretes glucocorticoids (cortisol and corticosterone); regulate carbohydrate metabolism by promoting gluconeogenesis; are useful in treating stress, autoimmune diseases, chronic inflammation, and in promoting acceptance of heterologous grafts; secretion is stimulated by ACTH
Side Effects of long term Glucocorticoid therapy
lymphopenia, eosinopenia, and neutrophilia.
Zona Reticularis (ZR)
Is the deepest layer of the cortex, constitutes only 7% of its total volume
What do the cells in the Zona Reticularis (ZR) of the Adrenal cortex secrete
Secretes weak androgens (dehydroepiandrosterone, and some androstenedione) and small amounts of glucocorticoids
How is the hormone production stimulated in the ZR
hormone production is stimulated by ACTH.
Adrenal androgens play an important role in the onset of puberty in humans, especially in the growth of pubic and axillary hairs.
The medulla of the Adrenal gland contains
Contains chromaffin cells, which are modified postganglionic sympathetic neurons and are innervated by the preganglionic sympathetic (cholinergic) fibers
; physiological effects include “fight-or-flight response”, increased blood pressure, faster heart rate, faster breathing rate, and elevated blood glucose level.
What do Chromaffin cells secrete
Secrete mostly epinephrine and some norepinephrine (different cell types)
physiological effects include “fight-or-flight response”, increased blood pressure, faster heart rate, faster breathing rate, and elevated blood glucose level
Difference between epinehrine cells and norepiniehrine cells histologicially (slide 26)
What mediates Catecholamine release
Catecholamine release is under nervous control, mediated by the preganglionic sympathetic fibers
Blood Supply to the Adrenal Gland
Cortical blood capillaries are fenestrated sinusoids;
medullary artery passes through the cortex and breaks into capillaries in the medulla;
both cortical sinusoids and medullary capillaries drain into medullary veins;
the latter join the suprarenal vein.
Clinical significance of adrenal gland
Cushing’s syndrome, characterized by hypersecretion of glucocorticoids: Addison’s disease, characterized by hyposecretion of adrenocortical hormones, is life threatening.
What is Addison’s disease
Characterized by hyposecretion of adrenocortical hormones, is life threatening.
Pineal Gland
Known as pineal body or epiphysis, projects from the roof of the diencephalon
What is the Pineal Gland Composed of
Composed of pinealocytes and neuroglia cells
What do pinealocytes secrete
Pinealocytes secrete melatonin
What is melatonin responsible for
Responsible for seasonal cyclicity observed in horses (long-day breeder) and sheep and goats (short-day breeder)
Argentaffin Cell secretions
Gastrin
CCK
Somatostatin
VIP
Where is Gastrin secreted
By Argentaffin cells in the:
Duodenum
Jejunum
Where is Secretin
By Argentaffin cells in the:
Duodenum
Jejunum
Ileum
Where is Cholecystokinin (CCK) secreted
By Argentaffin cells in the:
Duodenum
Jejunum
Ileum
Where is Somatostatin secreted
By Argentaffin cells from the:
Stomach to the colon
Where is Vasoactive Intestinal polypeptide (VIP) secreted
By Argentaffin cells from the:
Stomach to the colon
Types of Islet of Langerhans in the Pancreas
Beta Cells of Islets of Langerhans: 70%
Alpha cells of Islets of Langerhans:20%
Delta Cells of Islets of Langerhans:5%
What do Beta Cells of Islets of Langerhans secrete
Insulin
What do Alpha cells of Islets of Langerhans secrete
Glucagon
What do Delta Cells of Islets of Langerhans secrete
Somatostatin
What do the JG cells in the Kidney Secrete
JG cells( Juxtaglomerular cells) secrete Renin
1,25 dihydroxycholecalciferols (metabolite of Vitamin D) Erythropoietin
It is secreted in the Kidney but what cell is not known
What are JG cells
Are modified smooth muscle cells of the afferent arteriole and lie adjacent to macula densa
When do JG cells secrete renin
Jg cells secrete renin in response to low blood pressure or hypovolemia or hyponatremia and help in blood pressure regulation
When is Erythropoietin secreted
Is secreted in response to a decreased oxygen supply to the kidney
What cells in the testis synthesize and secrete hormones
Leydig Cells
Sertoli Cells
What do Leydig cells secrete
Testosterone
What do Sertoli cells secrete
Estrogen
Inhibin
What cells in the Ovary synthesize and secrete Hormones
Theca interna Cells
Granulosa Cells
Luteal Cells
What do Theca Interna Cells secrete
Theca Interna cells have LH receptors and secrete Testosterone
What do Granulosa Cells secrete
Estrogen
Inhibin
Relationship between Granulosa Cells and Theca interna Cells
Granulosa cells have FSH receptors which convert Testosterone into estrogen.
The estrogen is released into the antrum and the blood
What do Luteal Cells Secrete
Progesterone
What structures synthesize and secrete hormones in the Placenta
Endometrial cups (equine)
Chorionic Epithelium
What are Endometrial cups
Consists of modified chorionic epithelial cells that secrete eCG (FSH like)
What do chorionic epithelium in humans secrete
hCG(LH-like)
What do chorionic epithelium secrete
Progesterone
estrogen
Note: Placenta of all species secrete these
What in the uterus secretes hormones
Endometrium
What does the Endometrium do if pregnancy does not occur
Secretes prostaglandin F2-Alpha (PGF2-alpha)
which causes lysis of the corpus luteum, and thus the beginning of a new estrous cycle
What hormones do nerve synapses/ terminals secrete
Acetylcholine, norepinephrine
