Chapter 18: The Endocrine System Flashcards
1
Q
Hormone
A
A molecule that is releases in one part of the body that regulates the activity of cells in other parts of the body.
Most enter interstitial fluid and then the bloodstream.
2
Q
Exocrine Glands
A
Secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ, or to the outer surface of the body.
Includes: sudoriferous (sweat), sebaceous (oil), mucous, digestive glands.
3
Q
Endocrine Glands
A
Secrete their products into interstitial fluid surrounding the secretory cells rather than ducts. From here hormones diffuse into blood capillaries and blood carries them to target cells throughout the body.
4
Q
Endocrine System
A
All endocrine glands and hormone secreting cells. Acts on all types of cells.
Dependent on the cardiovascular system to distribute products (hormones).
5
Q
Hormone Receptors
A
Hormones travels throughout the body in blood, affecting a specific target cell. Hormones influxes their target cells by chemical binding to specific protein receptor.
Only the target cells for a given hormone have receptors that bind and recognize that hormone.
6
Q
Down-Regulation
A
Makes a target cell less sensitive to a hormone causing the target cells to decrease.
Receptors are constantly being synthesized and broken down.
Hormones present in excess, the number of target cell receptors may decrease.
.
7
Q
Up-Regulation
A
Makes a target cell more sensitive to a hormone so target cells will increase.
When a hormone is deficient, the number of receptors may increase.
8
Q
Circulating Hormones
A
Most endocrine hormones are circulating as they pass from the secretory cells that move them into interstitial fluid and then into the blood.
9
Q
Local Hormone
A
Other hormones. Example: interluekin-2
Act locally on neighboring cells or on the same cell that secreted them without entering the bloodstream.
When these hormones linger in blood, they are inactivated quickly.
10
Q
Paracrines
A
Local hormones that act on neighboring cells.
11
Q
Autocrines
A
Hormones that act on the same cell that secreted them.
12
Q
Steroid Hormone
A
Lipid Soluble
Derived from cholesterol.
Each steroid hormone is unique due to the presence of different chemical groups attached at various sites on 4 rings at the core of its structure.
These small differences allow for a large diversity of functions.
13
Q
Thyroid Hormones
A
Lipid Soluble
T3 and T4
Synthesized by attaching iodine to the amino acid tyrosine.
The presence of 2 benzene rings with a T3 or T4 molecule makes these hormones very lipid soluble.
14
Q
Nitric Oxide
A
Lipid Soluble
This gas is both a hormone and a neurotransmitter.
Synthesis is catalyzed by the enzyme nitric oxide synthase.
15
Q
Amine Hormones
A
Water Soluble
Synthesized by decarboxylating and otherwise modifying certain amino acids.
Called amines as they retain amino group NH3+.
Catecholamines: epi, norepi, dopamine are synthesized by tyrosine.
Histamine: synthesized from histidine by mast cells and platelets.
16
Q
Peptide and Protein Hormones
A
Water soluble
Amino acid polymers.
Peptide: 3-49 amino acids-antidiuretic hormone, oxytocin
Proteins: 50-200 amino acids- growth hormone, insulin
17
Q
Glycoproteins Hormone
A
Water soluble
Protein hormone
Example: thyroid stimulating hormone. Have attached carbohydrate groups.
18
Q
Eicosanoid Hormones
A
Water soluble
20 forms. Derived from arachidonic acid, 20 carbon fatty acid.
Are important local hormones. Act as circulating hormones.
2 types: prostaglandins (PGs) and Leukotrienes (LTs).
19
Q
Water Soluble Hormones in Blood
A
Most circulate in the watery blood plasma in free form (Not attached to other molecules).
20
Q
Lipid Soluble Hormones Transport in Blood
A
Most molecules are bound to transport proteins which are syntheses by cells in the liver.
21
Q
Transport Proteins in Blood
A
Have 3 functions
1. Make lipid soluble hormones temporarily water soluble thus increasing their solubility in blood.
2. Retard passage of small hormones molecules through the filtering mechanism in the kidneys, thus slowing the rate of the hormone loss in urine.
3. Provide a ready reserve of hormone, already present in the bloodstream.
22
Q
Free Fraction
A
Where 0.1-10% of molecules of lipid soluble hormones is not bound to transport proteins.
These molecules diffuses out of capillaries, bind to receptors and triggers responses.
When free hormones leave blood, transport proteins releases new ones to replenish the free fraction.
23
Q
Action of Lipid Soluble Hormones
A
- Free lipid soluble hormones diffuse from blood, through interstitial fluid, then through lipid bilayer of PM into a cell.
- Hormones bind to and activated receptors within the cytosol or nucleus. Hormone complex alters gene expression. (Turns on and off).
- Newly formed mRNA directs synthesis of specific proteins on ribosomes.
- New proteins alters cells activity and causes responses typical of that hormone.
24
Q
Action of Water Soluble Hormones
A
Water soluble hormones binds to receptors embedded in the PM of target cells
1. Binding of hormones (first messenger) to its receptor. Activates G protein, which activates adenylyl cyclase.
2. Activated adenylyl cyclase converts ATP to cAMP (second messenger).
3. cAMP serves as a second messenger to activate protein kinases.
4. Activated protein kinases phosphorylate cellular proteins.
5. Millions of phosphorylated proteins cause reactions that produce physiological responses.
6. Phosphiesterase inactivates cAM.
25
First Messenger
Where a water soluble “hormone” binds to its receptor at the outer surface of the plasma membrane.
26
Second Messenger
Produced by first messenger hormone inside the cell where a specific hormone stimulated responses take place.
When cAMP is being used by this messenger it will inactivate phosphodiesterase.
27
Hormone Interactions
Responsiveness of a target cell to a hormone depends on
1. Hormones concentration in the blood
2. Abundance of the target cells hormone receptors
3. Influences exerted by other hormones.
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Permissive Effect
Where actions of some hormones on target cells require a simultaneous or recent exposure to a second hormone.
29
Synergistic Effect
When the effector of 2 hormones act together is greater than the sum of their individual effects.
30
Antagonistic Effects
When one hormone opposites the actions of another hormone.
31
Hormone Secretion
Is regulated by
1. Signals from the nervous system
2. Chemical changes in the blood
3. Other hormones
32
Pituitary Gland
Endocrine gland. Pea shaped structure.
Secretes several hormones that control other endocrine glands.
Master is the hypothalamus. Small region below the thalamus and is a major link between nervous and endocrine system.
33
Anterior Pituitary
Or adenohypophysis
Secretes grimes that regulate wide range of bodily activities from growth to reproduction.
Accounts for 75 % of total weight of the gland and composed of epi tissue.
Consists of 2 parts;
1. Pars distails- larger portion
2. Pars tubealis- forms a sheath around the infundibulum
34
Posterior Pituitary
Or neurohypophysis
Composed of neural tissue.
Consist of 2 parts;
1. Pars nervosa- larger portion and infundibulum
2. Pars intermedia-thrid region, atrophies during human fetal development and ceases to exist as a separate lobe in adults
35
Growth Hormone (GH)
APH
Targets: liver
Actions: stimulates liver, muscle, cartilage, bone and other tissues to synthesize and secrete insulin like growth factors which
1. Increase growth of bones and soft tissue.
2. Acts directly on target cells to exchange lipolysis
3. Decrease glucose uptake.
36
Thyroid Stimulating Hormone (TSH)
APH
Target: thyroid gland
Actions: stimulates synthesis and secretion of thyroid hormones by thyroid gland.
37
Follicles Stimulating Hormones (FSH)
APH
Targets: ovary and testis
Actions: in females, initiates development of oocytes and induces ovarian secretion of estrogens.
In males, stimulates testes to produce sperm.
38
Luteinizing Hormones (LH)
APH
Target: ovary and testis
Action: in females, stimulates secretion of estrogen and progestones, ovulation and formation of corpus lutes.
In males, stimulates testes to produce testosterone.
39
Prolactin (PRL)
APH
Target: mammary glands
Actions: together with other hormones, promotes milk production by mammary glands.
40
Adrenocorticotropic Hormone (ACTH)
APH
Targets: adrenal Cortex
Actions: stimulates secretion of glucocorticoids (mainly cortisol) by adrenal cortex.
If there was an increased amount of cortisol in blood, the level of ACTh would decrease.
41
Melanocytes Stimulating Hormone (MSH)
APH
Targets: brain
Action: exact role in humans in unknown but may influence brain activity. When present in excess can cause darkening of skin.
42
Insulin Like Growth Factors (IGFs)
Small protein hormone, synthesized in the liver.
GH exerts its growth promoting effects indirectly through this hormone.
This hormone is secreted in response to GH from cells in the liver, skeletal muscles, cartilage and bones.
43
Tropic Hormones
Anterior pituitary hormones that act on other endocrine glands.
44
Inhibiting Hormones
Produced by the hypothalamus, suppress secretion of anterior pituitary hormones.
1. Growth hormone inhibiting hormone (GHIH): or somatostatin, inhibiting secretion of growth hormone.
2. Prolactin inhibiting home (PIH): dopamine, suppresses secretion of prolactin.
45
Hypophyseal Portal System
Blood flows from capillaries in the hypothalamus into portal vein that carry blood to capillaries of the anterior pituitary (adenohpophysis).
The hormones carried allow for communication and are an important link between the nervous and the endocrine system.
46
Superior Hypophyseal Arteries
Branches of the internal carotid arteries, brings blood into the hypothalamus.
47
Primary Plexus of the Hypophyseal Portal System
Capillary network where arteries divide at the junction of the median eminence of the hypothalamus and the infundibulum.
48
Hypophyseal Portal Veins
Blood drains into this vein from the primary plexus that pass down the outside of the infundibulum.
49
Secondary Plexus of the Hypophyseal Portal System
Another capillaries network that is formed where the Hypophyseal portal vein divides in the anterior pituitary.
50
Hypophyseal Veins
Drain blood from the anterior pituitary.
51
Neurosecretory Cells
Clusters of neurons that are located above the optic chias.
52
Posterior Pituitary
Does not synthesize hormones.
Stores and release 2 hormones:
(1) oxytocin (2) anti diuretic hormone
Consists of: axons and axons terminals of more than 10,000 hypothalamic Neurosecretory cells.
53
Paraventricular and Supraoptic Nuclei
Contains the cell bodies of Neurosecretory cells of the hypothalamus.
Cell bodies synthesize the hormones: oxytocin (OT) and anti diuretic hormone (ADH) or vasopressin.
54
Hypothalamic-Hypophyseal Tract
Formed by Paraventricular and supraoptic nuclei axons.
Tract begins in the hypothalamus and ends near the blood capillaries in the posterior pituitary.
55
Pituicytes
Specialized Neuroglia that is associated with axon terminals in the posterior pituitary.
56
Inferior Hypophyseal Arteries
Supplies blood to the posterior pituitary which branch from the internal carotid arteries.
57
Capillary Plexus of the Infundibulum Process
A capillary network that receives secreted O2 and anti directed hormone.
The inferior Hypophyseal arteries drain into this process.
From this plexus, hormones pass into the Hypophyseal veins for distribution to target cells in other tissues.
58
Osmoreceptors
Detects high blood osmolarity.
These neurons are located in the hypothalamus and monitors changes in blood osmolarity.
59
Oxytocin (OT)
PH
Hypothalamus secrete this hormone in response to uterine distant ion and stimulation of nipples.
Stimulates contraction of smooth muscle cells in the uterus during childbirth.
Stimulates contractions of myoepithelial cells in mammary glands to cause milk ejection.
60
Antidiuretic Hormone (ADH)
PH
Hypothalamus secretes ADH in response to elevated blood osmotic pressure, dehydration, loss of blood volume, pain or stress.
Conserves body water by decreasing urine volume and perspiration.
Raises BP by constricting arterioles.
61
Thyroid Glands
Butterfly shaped glands. Located just inferior to the larynx.
Composed of left and right lateral lobes on either side of the trachea.
As cells produce and use more ATP their increase BMR (Basel metabolic rate)
62
Isthmus
Connect the right and left lateral lobes of the thyroid gland.
63
Thyroid Follicles
Microscopic spherical sacs. Make up most of the thyroid gland. Basement membrane surrounds each follicle.
64
Follicular Cells
Primary cells located in the wall of each follicle. They extend to the lumen (internal space) of the follicle.
Secrete T3 and T4. Transports iodide ions from the blood into the crystal.
65
Thyroxine and Triiodothyronine
Thyroxine also known as T4: tetraiodothyronine
Produced by the follicular cells. Secreted in response to low thyroid hormone levels, low metabolic rate, cold, pregnancy and high altitudes.
Increases BMR, stimulate synthesis of proteins. Increase use of glucose and fatty acids for ATP production.
Increase lipolysis.
66
Thyroid Horomes
T3 and T4
67
Parafollicular Cells
Or C cells
Lie between the thyroid follicles
Produce hormone calcitonin.
68
Calcitonin
Secreted by parafollicular cells in thyroid follicles.
Helps regulate calcium homeostasis.
High blood Ca2+ levels stimulate secretion, low levels inhibit secretion.
Lowers blood levels of Ca2+ and HPO4 2- by inhibiting bone resorption by osteoclasts and by accelerating uptake of calcium and phosphates into bone extracellular matrix.
69
Actions of Thyroid Hormone
Most cells have receptors for thyroid hormones T3 and T4
1. Increase basal metabolic rate (BMR): the rate of energy expenditure under standard or basal conditions (awake, at rest and fasting). When BMR increase, cellular metabolism of carbs, lipids and portion increases.
2. Enhance action of catecholamines (epi and norepinephrine) permissive effects because they up regulate B-Adrenergic receptors. Causes increased HR, and BP.
3. Regulate development and growth of nervous tissue and bones: promotes synapse formation, myelin production and growth of dendrites. Promotes formation of ossification centers in developing bones.
70
Parathyroid Glands
Partially embedded in the posterior surface of the lateral lobes of the thyroid glands.
Small round masses of tissue.
Contains:
chief cells: produce PTH. PTH is regulated by anterior pituitary.
oxyphil cells. These cells do not have a defined function in a healthy adult. Secrete PTH in cancer of the gland.
71
Parathyroid Hormone (PTH)
Produced in chief cells. Controlled by a negative feedback loop: secretion is controlled by chemical changes in the blood like low amounts of Ca2+.
Major regulator of levels of ca2+, mg2+ and phosphate (HPO4 2-) ions in blood.
Promotes formation of Calcitrol active form of vitamin D.
Increases the number and activity of osteoclasts.
Results in relocated bone respiration which released calcium and phosphates into the blood.
72
Calcitriol
Active form of vitamin D.
When PTH acts on the kidneys it promotes the formation of this hormone.
Increase rate of ca2+ and HPO4 2- and mg absorption from the GI tract into the blood.
If there is too much Ca2+ in blood, Calcitriol levels would decrease.
73
Adrenal Glands
Paired, one lies superior to each kidney in the retroperitoneal space.
Have a flattened pyramidal shape.
Contains adrenal cortex and adrenal medulla.
74
Adrenal Coretx
Larger peripherally located.
Regulated by hormones.
Subdivided into 3 zones that secrete different hormones.
1. Zona glomerulosa: cells are closely packed and arranged in spherical clusters/arched columns. Secretes mineralocorticoids.
2. Zona fasciculate: widest zone. Consists of cells arranged in long straight columns. Secrete glucocorticoids.
3. Zona reticular is: arranged in branching cords. Synthesize small amounts of androgens.
75
Aldosterone
Adrenal gland hormone: Zona glomerulosa cells
Major mineralocorticoids
Regulates homeostasis of 2 mineral ions: sodium and potassium. Increases blood levels of Na and decreases blood level of K.
Promotes excretions of H in the urine, this removes acids from the body can help prevent acidosis.
76
Glucocorticoids
Adrenal gland: Zona Fasciculata cells
Regulate metabolism and resistance to stress. Increase protein breakdown, depression immune responses.
Include: cortisol, corticosterone’s cortisone.
Most abundant: cortisol, accounts for 95% of glucocorticoids activity.
77
Glucocorticoids Effects
1. Protein breakdown: mainly in muscle fibers, thus increasing liberation of amino acids into the bloodstream. Amino acid can be used to synthesize new proteins for ATP.
2. Glucose formation: liver cells will convert amino acids or lactic acid to glucose that can be used for ATP.
3. Lipolysis: stimulates lipolysis. Breakdown for triglycerides and release fatty acids from adipose tissue into blood.
4. Resistance to stress: liver cells provide tissue with ATP to combat stress. Causes vasoconstriction to raise BP when major blood loss occurs.
5. Anti-inflammatory effects: inhibit WBC that participate in inflammatory response. Very useful in treatment of chronic inflammatory disorders.
6. Depression of immune responses: in high doses, dress immune response. Used in organ transplant recipients.
78
Control of Glucocorticoids Secretion
Occurs via a negative feedback loop.
Low blood levels of glucocorticoids mainly cortisol stimulate Neurosecretory cells in the hypothalamus to secrete:
Corticotropin releasing hormone (CRH).
CRH promotes the releases of ACTH from anterior pituitary. ACTH flows in the blood to the adrenal cortex, where it stimulates glucocorticoids secretion.
79
Adrenal Medulla
Inner region of adrenal gland, secretes horomes.
Hormone producing cells: chromaffin cells
Regulated by neural stimuli
Modified sympathetic ganglion of the ANS.
Two major hormones synthesized: 20 % norepinephrine and 80% epinephrine.
80
Androgens
Adrenal glands Hormone
From Zona reticularis
Assist in early growth of axillary and pubic hair in both sexes. In females contributes to libido and menopause.
81
Epinephrine and Norepinephrine
Adrenal Medulla hormones
From chromaffin cells
Enhance effects of sympathetic division of ANS during stress.
82
Pancreas
Both an endocrine and exocrine gland.
Located in the curve of the duodenum, first part of the small intestine. Consists of a head, body and tail.
83
Acini
Cluster of exocrine cells of the pancreas.
Produce digestive enzymes which flow into the GI tract through a network of ducts.
84
Pancreatic Islets
Found scattered amount the acini. 1-2 million tiny clusters of endocrine tissue.
85
Cell Types in Pancreatic Islet
1. Alpha cells: 17% secrete glucagon
2. Beta cells: 70% secrete insulin
3. Delta cells: 7% secrete somatosatin
4. F cells: 6% secrete pancreatic polypeptide; Secretion is stimulated by meals with protein, exercise, hypglucemia
86
Insulin Secretion
Stimulated by:
1. Acetylcholine, liberated from axon terminals. Nerve fivers innervate the pancreatic islet.
2. Amino acids arginine and leucine. Present in blood after eating high protein meal
3. Glucose dependent insulinotropic, hormones released by enteroendrocrine cells of small intestine in repose to glucose in the GI tract.
87
Glucagon Secretion
Acts on heptaocytes (liver cell) to breakdown glycogen into glucose in the liver.
Stimulated by:
1. Increased activity of the sympathetic division of the ANS, occurs during exercise.
2. A rise in blood amino acids if glucose levels are low.
88
Glucagon
Alpha cells
Raises blood glucose levels by accelerating breakdown of glycogen into glucose in the liver and releasing it into blood.
89
Insulin
Beta cells
Lowers blood glucose levels by accelerating transport of glucose into cells
90
Somatostatin
From Delta cells
Inhibits secretion of insulin and glucagon, slow absorption of nutrients from GI Tract.
91
Pancreatic Polypeptide
From F cells
Inhibits somatostatin secretion, gallbladder contraction and secretion of pancreatic digestive enzymes.
92
Gonads
Organs that produce gametes. Sperm in males and oocytes in females.
Produce inhibin in both sexes.
93
Ovaries
Parceled oval bodies located in the female pelvic cavity. Produce hormones: estrogen and progesterone.
94
Testes
Male gonads, oval glands that lie in the scrotum. Main hormone produces and secretes testosterone and Androgen.
95
Estrogen and Progesterone
Ovarian Hormones
Together with gonadotropic hormones of anterior pituitary , regulate female reproductive cycle
maintain pregnancy
prepare mammary glands for lactation
Promote development of female secondary sex characteristics.
96
Relaxin (RLX)
Ovarian Hormones
Type of peptide horome
Increases flex ability of pubic symphysis during pregnancy
Help dilate uterine cervix (enlarged the birth canal) during labor and delivery.
97
Inhibin
Ovarian Hormone
Type of protein hormone.
Inhibits secretion of FSH from anterior pituitary.
98
Testosterone
Testicular hormones
Stimulates decent of testes before birth
Regulates sperm production
Promotes development and maintenance of male secondary sex characteristics.
99
Pineal Glands
Small endocrine gland attached to the roof of the third ventricle of the brain at the mideline.
Secretes: melatonin
100
Pinealocytes
Masses of Neuroglia and secretory cells of the pineal gland.
Secretes amine hormone: melatonin
101
Melatonin
Secreted by the pineal gland.
Amine hormone derived from serotonin. Contributes to the setting of the body’s biological clock.
102
Thymus
Located behind the sternum between the lungs
Plays a role in immunity.
Produces:
Thymosin
Thymic humeral factor (THF)
Thymic factor (TF)
Thymopoietin
Promote the maturation of T cells
103
Prostaglandins (PG) and Leukotrienes (LTs)
Eicosanoids
Found in the body except in RBCs. Act as local hormones in response to chemical or mechanical stimuli.
104
Cholecalciferol
Skin hormone
Plays a role in the synthesis of Calcitriol, active form of vitamin D.
105
Gastric
GI Tract hormone
Promotes secretion of gastric juices, increase movements of the stomach.
106
Glucose Dependent Insulinotropic Peptide (GIP)
GI Tract hormone
Stimulates releases of insulin by pancreatic beta cells.
107
Secretin
GI tract hormone
Stimulates secretion of pancreatic juice and bile.
108
Cholecystokinin (CCK)
Secreted by GI Tract
Stimulates secretion of pancreatic juice
Regulates releases of bile from gallbladder
Causes feeling of fullness after eating.
109
Human Chorionic Gonadotropin (hCG)
Placenta Hormone
Stimulates corpus luteum in ovary to continue production of estrogens and progesterone to maintain pregnancy.
110
Human Chorionic Somatomammotropin (hCS)
Placenta Hormone
Stimulates development of mammary glands for lactation.
111
Renin
Kidney hormone
Part of reaction sequence that raises blood pressure by brining about vasoconstriction and secretion of aldosterone.
112
Erythropoietin (EPO)
Kidney Hormone
Increases rate of red blood cell formation.
If damage to kidney occurs, anemia would offer due to decreased red blood cell formation.
113
Calcitriol
Kidney hormone
Active form of vitamin D
Aids in absorption of dietary calcium and phosphorus.
114
Atrial Natriuretic Peptide (ANP)
Heart Hormone
Decrease blood pressure.
115
Lepton
Adipose Tissue hormone
Suppresses appetites
May increase FSH and LH activity.
116
Growth Factors
Play important roles in tissue development, growth and repair.
Are mitogenic substances, they cause growth by stimulating cell division.
117
Eustress
Prepares us to meet certain challenges and is helpful.
118
Distress
Harmful stress
119
Stressor
Any stimulus that produces a stress response.
Prolonged stress decrease the immune system/
120
Stress Response
Changes that happen during stress conditions. Are controlled by the hypothalamus.
Occurs in 3 stages:
1. Fight or flight response ( initiated by nerve impulses of the hypothalamus). Epi and norepinephrine are released. Causes sweaty hands, increased BP,HR.
2. Slower resistance reaction (releases hormones in order to fight stressors after the fight or flight)
3. Exhaustion (begins when resistance stage fails)
Effects of stress Response: increased HR, affect functions of blood vessels, increase BP.
121
Thyroid Releasing Hormone (TRH)
Production of this hormone is inhibited by T3 and T4 in the negative feedback loop. IF thyroid gland is removed there would be higher levels of TRH in the bloodstream due to t3 and t4 not being releases to inhibit TRH.
122
Characteristics of Endocrine and Nervous Systems have in Common
Both have effects that are excreted on target cells by binding to specific receptors.
123
Suprarenal Medulla
During fight or flight responses, the SNS responds to stressful situations via nerve impulses of sympathetic neurons that simulate cells in this medulla to release epinephrine and norepinephrine.
124
Secretin and Cholecystokinin
Common function: to stimulate secretion and regulation of bile.
125
Platelet-Derived Growth Factors (PDGFs)
Plays a role in wound healing.
126
Water Soluble Hormones
Bind to membrane receptors.
127
Lipid Soluble Hormones
Bind to intracellular receptors.
128
Adenylate Cyclase
This is activated when G protein is activated.
Converts ATP into cyclic AMP (cAMP). This process occurs because water soluble hormone are unable to diffuse through lipid bilayer of PM of their target cells.
129
Somatocrinin
Hypothalamic releasing hormone or growth releasing hormone
Stimulates the secretion of human growth hormone (HGH).
130
2 glands responsible for calcium homeostasis
Thyroid and parathyroid gland.
Thyroid secretes calcitonin from parafollicular cells
parathyroid secretes PTH from chief cells
Calcitonin and PTH have an antagonistic effect as calcitonin inhibits osteoclasts activity decreasing ca2+ levels.
