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MB prep: Physiology > Endocrinology > Flashcards

Endocrinology Flashcards

1
Q

WHAT IS A HORMONE

A

A hormone is a specific organic chemical produced within, and secreted by certain cells directly into the ECF (extracellular fluid) for transmission to a target organ and/or tissues, where it exerts one or more specific physiologic effects (or simply put; a chemical regulatory substance)

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2
Q

INTRODUCE ENDOCRINOLOGY

A

-The complex activities of the human body are strictly regulated, coordinated and integrated. So that no particular activity is in excess or at an insufficient or ineffectual level
-Two systems are responsible for this strict control;
a). Nervous system whose control is via electric impulses conducted rapidly in nerves. Fast, with short-lived effects (telephone)
b). Endocrine system whose control is slower in onset, with more prolonged and generally widespread effects (letter)
- These two systems are linked through the hypothalamus (which controls the secretion of many of the endocrine glands)
- The endocrine system exerts its effect through the secretion of chemical messengers called hormones.

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3
Q

what are endocrine glands

A

they are ductless glands that secrete thier hormones into the blood stream to their target tissues.

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4
Q

if you are asked to discuss hormones, outline the steps

A

define hormones
Nature of hormones
Classification of hormones
Formation of hormones
Mechanism of action of hormones

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5
Q

what is a local hormone

A

These are not produced by a specific glandular organ, but yet exert its action either locally or at a distance from the cell or tissue in which it is produced
They are synthesized, utilized and inactivated in a restricted area.

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6
Q

examples of local hormones

A

-Acetylcholine
-Adrenaline
-Noradrenaline
-Histamine
-Erythropoietin
-Cholecystokinin, Gastrin, Secretin and Renin (GIT hormones)
-Serotonin
-1,25 Dihydroxycholecalciferol

~Hypothalamic Releasing Hormones:

-Thyrotropin-Releasing Factor (TRF)
-Luteotropic Hormone-Releasing Factor (LHRF)
-Follicle-Stimulating Hormone Releasing Factor (FSHRF)
-Adrenocorticotropin-Releasing Factor (ARF)
-Somatotropin-Releasing Factor (SRF)
-Prolactin-Releasing Factor (PRF)
-Hypothalamic inhibiting hormone
-Growth Hormone Release-Inhibiting Factor (GH-RIF)
-Prolactin Inhibiting Factor (PIF)
-Gamma-Aminobutyric Acid (GABA)

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7
Q

what are general hormones

A
  • synthesized by specific ductless endocrine glands, are secreted directly into the stream of blood perfusing these glands
  • Once released into the bloodstream, general hormones are transported via the cardiovascular system to other regions of the body where they produce their effects
  • These hormones are classified as proteins, peptides, amino acid derivatives and steroids
  • Their concentration in the blood is always very small
  • Most exert their effects upon tissues which are located far from their site of production
  • A hormone may act on a specific target organ or it may exert its effect on most or all tissues
  • Hormones do not initiate reactions, but modify the rates of reactions already occurring
  • Most hormones are continuously secreted at basal rates, these rates can be increased or decreased by appropriate stimuli to the endocrine glands
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8
Q

list endocrine organs that secrete general hormones

A

-Anterior Pituitary Gland
-Posterior Pituitary Gland
-Thyroid Gland
-Parathyroid Gland
-Adrenal Cortex
-Islets of Langerhans in the pancreas
-Ovary
-Testis

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9
Q

list hormones from the anterior pituitary

A
  1. Growth hormone (GH)
  2. Thyroid­ stimulating hormone (TSH)
  3. Adrenocorticotropic hormone (ACTH)
  4. Follicle-stimulating hormone (FSH)
  5. Luteinizing hormone (LH)
  6. Prolactin
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10
Q

list hormones from posterior pitituary

A
  1. Antidiuretic hormone (ADH)
  2. Oxytocin
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11
Q

list hormones from the thyroid gland

A
  1. Thyroxine (T4)
  2. Triiodothyronine (T3)
  3. Calcitonin
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12
Q

LIST HORMONE FROM the parathyroid gland

A

parathormone

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13
Q

list hormones from the pancreas

A
  1. Insulin
  2. Glucagon
  3. Somatostatin
  4. Pancreatic polypeptide
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14
Q

list hormones of the adrenal cortex

A

-Mineralocorticoids
1. Aldosterone
2. 11­deoxycorticosterone

-Glucocorticoids
1. Cortisol
2. Corticosterone

  • Sex hormones
    1. Androgens
    2. Estrogen
    3. Progesterone
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15
Q

list hormones of the adrenal cortex

A

-Mineralocorticoids
1. Aldosterone
2. 11­deoxycorticosterone

-Glucocorticoids
1. Cortisol
2. Corticosterone

-Sex hormones
1. Androgens
2. Estrogen
3. Progesterone

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16
Q

list hormones of the adrenal medulla

A
  1. Catecholamines:
  2. Adrenaline (Epinephrine)
  3. Noradrenaline (Norepinephrine)
  4. Dopamine
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17
Q

list hormones from the testis

A
  1. Testosterone
  2. Dihydrotestosterone
  3. Androstenedion
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18
Q

list hormones from the ovary

A
  1. Estrogen
  2. Progesterone
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19
Q

list hormones from the pineal gland

A

melatonin

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20
Q

list hormones from the thymus

A
  1. Thymosin
  2. Thymin
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21
Q

list hormones from the kidney

A
  1. Erythropoietin
  2. Thrombopoietin
  3. Renin
  4. 1,25­dihydroxycholecalciferol (calcitriol)
  5. Prostaglandins
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22
Q

list hormones from the heart

A
  1. Atrial natriuretic peptide
  2. Brain natriuretic peptide
  3. C­type natriuretic peptide
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23
Q

list hormones from the placenta

A
  1. Human chorionic gonadotropin (HCG)
  2. Human chorionic somatomammotropin
  3. Estrogen
  4. Progesterone
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24
Q

based on the chemical structure, what are the classes of hormones?

A

-steroid hormones
-protein/ peptide hormones
-hormones derived from the amino acid tyrosine

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25
Q

list steroid hormones you know

A

Aldosterone
11-deoxycorticosterone
Cortisol
Corticosterone
Testosterone
Dihydrotestosterone
Dehydroepiandrosterone
Androstenedione
Estrogen
Progesterone

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26
Q

list protein hormones you know

A

Growth hormone (GH)
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin
Antidiuretic hormone (ADH)
Oxytocin
Parathormone
Calcitonin
Insulin
Glucagon
Somatostatin
Pancreatic polypeptide
Human chorionic gonadotropin (HCG)
Human chorionic somatomammotropin.

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27
Q

hormones derived from amino acid tyrosin that you know

A

Thyroxine (T4)
Triiodothyronine (T3)
Adrenaline (Epinephrine)
Noradrenaline (Norepinephrine)
Dopamine.

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28
Q

what glands secrete steroid hormones

A

i.Adrenal cortical hormones
ii.Hormones of the ovaries
iii.Hormone of the testes
iv.Hormones of the placenta (Oestrogen and progesterone only)

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29
Q

what glands secrete protein hormones

A

-Parafollicular cells of thyroid gland (Calcitonin)
-Parathyroid gland
-Anterior pituitary gland
-Posterior pituitary gland
-Pancreas
-Plancenta (Human Chorionic Gonadotropin, Human Chorionic Somatomammotropin)

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30
Q

what glands secrete hormones derived from tyrosine

A

Thyroid glands
Adrenal Medulla

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31
Q

How are protein hormones formed

A

-All protein hormones are formed by the granular endoplasmic reticulum
-Synthesis is initiated in the nucleus of the endocrine cell
-Nuclear DNA initiates the formation of the active mRNA and tRNA
-tRNA acts on cytoplasmic rough endoplasmic reticulum to cause synthesis of the appropriate protein
-Initially protein hormones are formed as inactive proteins (pro-hormones)
-Pro-hormones are larger in size than the active hormones
-Some part of this inactive hormone precursor is removed before the active hormone is released
-The active hormone is then packaged into small membrane encapsulated vesicles called secretory vesicles or secretory granules
-The hormone is stored in this packaged form in the cytoplasm of the endocrine gland until the stimulus for its release is received by the endocrine gland

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32
Q

how are tyrosine-derived hormones formed

A

-Formed by enzymatic reactions in the cytoplasmic compartments of the glandular cells
-The hormones formed are stored in the glands in which they are formed until the stimuli for their release are received

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33
Q

how are steroid hormones formed

A

-Only small amounts are stored in relevant endocrine glands
-A large amount of precursor molecules is present in these endocrine glands
-These precursor molecules can be rapidly converted to the final hormones when the need to release these hormones into the circulation arises
-Stimuli to these glands initiate the synthesis of the hormones, which are released into the blood stream as soon as they are manufactured

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34
Q

how is the rate of release of a hormone regulated

A

NEGATIVE FEEDBACK MECHANISM
-An endocrine gland normally produces its hormone and this hormone goes to the target organ to exert its effects
-Rate of hormone production increases steadily until it is adequate for the function the hormone is to perform
-When this signal is becoming excessive, some factors in the body send a signal back to the endocrine gland and cause a negative effect on the gland leading to a decrease in its rate of secretion
-It is only when the target organ’s activity rises to an appropriate level that the feedback to the gland becomes powerful enough to cause a decrease in further production of the hormone
-The signal that comes back to the gland to cause a decrease in its secretion is referred to as a negative feedback mechanism

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35
Q

what is the role of receptors in the action of hormones

A

-Hormones do not act directly on the target organs
-They act through combination with hormone receptors which are located on the cell surface or inside the cells
-Hormonal receptors are very large proteins, hormones with similar molecular structures may produce overlapping physiological responses.
-The presence or absence of receptor molecules in a cell membrane (or within the cell in some cases) determines whether or not that cell is sensitive to a particular hormone (specificity)
-Each receptor is highly specific for a single hormone, hence the target tissues that are affected by a hormone are those that contain its specific receptors

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36
Q

what hormone receptors are in the cell membrane

A

Receptors of protein hormones and adrenal medullary hormones (catecholamines) are situated in the cell membrane

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37
Q

what receptors are located in the cell cytoplasm

A

steroid hormones

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38
Q

what receptors are in the cell nucleus

A

Thyrosine derived hormones

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39
Q

how are receptors regulated

A

Generally, when a hormone is secreted in excess, the number of receptors of that hormone decreases due to binding of hormone with receptors. This process is called down-regulation. During the hormone deficiency, the receptor number increases, called upregulation.

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40
Q

what are the first messengers in Hormone action

A

The hormone which acts on a target cell, is called first
messenger or chemical mediator. It combines with the
receptor and forms a hormone-receptor complex.
The receptors exert actions that could activate cytoplasmic systems which then produce “second messengers”

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41
Q

what hormones act on the intracellular enzymes for their mechanism of action

A

Protein hormones and the catecholamines

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42
Q

what hormones act on the genes for their mechanism of action

A

Thryrosine-derived hormones and steroid hormones

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43
Q

outline the processes for the mechanism of action of protein hormones and catecholamines

A

-Protein hormones and catecholamines (First messenger) are water-soluble hormones and thus membrane insoluble, they thus bind to specific cell membrane receptors .

-The Hormone-receptor complex activates G-protein

-The activated G-Protein activates adenyl cyclase

-Adenyl cyclase catalyses the conversion of ATP to cAMP (The secondary messenger)

-cAMP activates protein kinases

-Protein Kinase phosphorylates proteins in the cytoplasm. This activates this enzymes allowing them to alter cell activity. They would produce changes like:

i. Contraction and relaxation of muscle fibers
ii. Alteration in the permeability of cell membrane
iii. Synthesis of substances inside the cell
iv. Secretion or release of substances by target cell
v. Other physiological activities of the target cell.

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44
Q

what changes does cAMP as second messenger

A

i. Contraction and relaxation of muscle fibers
ii. Alteration in the permeability of cell membrane
iii. Synthesis of substances inside the cell
iv. Secretion or release of substances by target cell
v. Other physiological activities of the target cell.

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45
Q

What are some second messengers you know

A

-Calcium ions and Calmodulin
-cAMP
-cGMP
-Products of membrane phospholipid breakdown (Intotisol triphosphate, diacylglycerol)

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46
Q

talk on the action of calcium and calmodulin as a second messenger

A

-Entry of Ca2+ into the cells initiates another second messenger system

-Ca2+ binds with a protein called calmodulin which has 4 separate calcium ion binding sites

-When 3 or all 4 sites have been bound with calcium, the calmodulin becomes activated and this leads to multiple physiological responses inside the cell in a manner similar to those caused by cAMP

-It activates many enzymes different from those activated by cAMP, leading to additional set of intracellular metabolic reactions

-Calmodulin activates myosin kinase which then acts directly on the myosin of smooth muscle leading to smooth muscle contraction

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47
Q

mechanism of action of inotisol triphosphate

A

Inositol triphosphate (IP3) is formed from phosphatidylinositol biphosphate (PIP2).Hormone-receptor complex activates the enzyme phospholipase, which converts PIP2 into IP3. IP3 acts on protein kinase C and causes the physiological response by the release of calcium ions into the cytoplasm of target cell.

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48
Q

mechaism of action of diacylglycerol

A

Diacylglycerol (DAG) is also produced from PIP2. It acts via protein kinase C

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49
Q

mechanism of action of cGMP

A

Cyclic guanosine monophosphate (cGMP) functions like cAMP by acting on protein kinase A

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50
Q

what is the mechanism of action of steroid hormones

A

ACTING ON GENES
-Steroid hormone enters the cell cytoplasm and binds with specific receptor proteins in the cytoplasm

-The hormone/receptor protein complex then diffuses into or is transported into the cell nucleus

-Inside the nucleus, the complex combines with nuclear DNA thus activating specific genes to form messenger RNA (mRNA)

-The mRNA diffuses out of the nucleus and reaches ribosomes and activates them

-Activated ribosomes produce large quantities of
proteins

-These proteins then produce physiological changes in the target cells:
-function as enzymes,
-transport proteins or structural proteins that in turn provide other functions of the cells

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51
Q

outline the mechanism of action of thyroid hormones

A

ACTING ON THE GENES
-Thyroid hormones (Thyroxine and triiodothyronine) pass through the cell membrane and bind to specific receptor proteins on the cell nucleus.

-The hormone receptor complex moves towards DNA and activates the DNA.

-This causes the transcription of mRNA

-The mRNA moves out of the cell nucleus and activates the ribosomes

-Activated ribosomes produce proteins

-These proteins produce physiological changes in the target cell. Many of these proteins are intracellular enzymes that cause enhanced metabolic activity in most cells of the body.

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52
Q

How are hormones inactivated/degraded, excreted?

A

Once a hormone produces its effects its necessary that its removed from the bloodstream.
-The process of inactivation may take place in the target organ, in the liver or in the kidney

-The liver is the most important site of hormone inactivation because the liver metabolizes many hormones, conjugating them with glucuronide or sulphate

-The water-soluble conjugates are then secreted into the bile and excreted in the faeces or the conjugates may enter the bloodstream to be excreted by the kidneys

-The kidneys also inactivate some hormones and excrete the inactivated metabolites

-Some low molecular weight hormones can be excreted directly into the urine.

-The lactating mammary gland has been implicated in the inactivation and excretion of oxytocin

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53
Q

what is the significance of an assay?

A

The assay (an analytic investigative procedure in laboratory medicine) of hormones or their metabolites in the urine is of great value in clinical medicine and research in assessing the secretion level of their endocrine glands

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54
Q

what are some notable examples of assays

A

-measurement of HCG (Human Chorionic Gonadotropin) in urine is used in early diagnosis of pregnancy.

-The urinary excretion of pregnanediol, and inactive metabolites of progesterone can be used in determining the hormonal status of the fetoplacental unit during pregnancy

-24hrs urine assay of vanillylmandelic acid (VMA) can be useful in the diagnosis of the adrenal gland tumour called phaechromocytoma

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55
Q

measurement of HCG in urine is for

A

early diagnosis of pregnncy

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56
Q

detection/ measurement of pregnanediol, and active metabolites of progesterone in urine is used for

A

determining the hormonal status of the fetoplacental unit in pregnancy

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57
Q

24hrs urine assay of vanillylmandelic acid(VMA) is useful for

A

diagnosis of adrenal gland tumour called phaechromocytoma

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58
Q

what is an indicator of adrenal gland tumour(pheochromocytoma) in urine?

A

vanillylmandelic acid(VMA)

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59
Q

what is the pituitary gland

A

-Pituitary gland is also called hypophysis
-A small gland, 1cm (diameter), 0.5-1gm (weight)
-Lies in a bony cavity (Sella turcica) at the base of the brain
-It’s connection to the hypothalamus is the pituitary/hypophysial stalk
-Physiologically its divisible into:
-Anterior pituitary
-Posterior pituitary

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60
Q

where does the pituitary gland lie

A

a bony cavity (sella turcica) at the base of the brain

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61
Q

what is the pituitary gland connection to the hypothalamus

A

The pituitary/ hypophyseal stalk

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62
Q

describe the anterior pituitary gland

A

Also called Adenohypophysis
-Embryologically originates from the Rathke’s pouch (an invagination of the pharyngeal epithelium); thus, the epithelioid nature of its cells

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63
Q

what is the embryonic origin of the pituitary gland

A

The Rathke’s pouch (an invagination of the pharyngeal epithelium), thus its epitheloid nature.

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64
Q

what is the posterior pituitary

A

also called Neurohypophysis
- Embryologically; neural tissue outgrowth from the hypothalamus, therefore, large number of glial-type cells are found in this gland.

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65
Q

what is the embryonic origin of the posterior pituitary

A

neural tissue outgrowth from the hypothalamus, therefore, large number of glial-type cells are found in this gland.

66
Q

what separates the anterior pituitary gland from the posterior pituitary

A

-Pars intermedia; relatively avascular zone between the Anterior pituitary gland and Posterior pituitary gland, almost absent in humans, but larger and more functional in lower animals.

67
Q

what anterior pituitary hormones have inhibitory hormones

A

Prolactin: prolactin inhibitory hormones
GH: Growth hormone inhibitory hormone

68
Q

by vascular connections, what relates the anterior pituitary to the hypothalamus

A

median eminence

69
Q

the bodies of the cells that secrete the posterior pituitary hormones are where

A

hypothalamus, they are called the magnocellular neurons

70
Q

the cells that secrete the posterior pituitary hormones are called what

A

magnocellular neurons

71
Q

where are the magnocellular neurons of ADH located

A

supraoptic nucleus of the hypothalamus

72
Q

the supraoptic nucleus produces which hormone

A

ADH

73
Q

where are the magnocellular neurons of oxytocin located

A

The paraventricular nuclei of the hypothalamus

74
Q

the paraventricular nuclei of the hypothalamus produce what hormone

A

oxytocin

75
Q

hormone release from the posterior pituitary is due to what

A

nerve impulses from hypothalamus

76
Q

what cells produce GH

A

Somatotropes

77
Q

somatotropes stain?

A

acidically, i.e with acid dyes (also called acidotropes)

78
Q

what percentage of the anterior pituitary gland cells are the somatotropes

A

30-40%

79
Q

how many amino acids is GH

A

single chain peptide with 191 amino acids

80
Q

what is the molecular weight of GH

A

21500

81
Q

What is the GH level in human

A

In small pikin: 6ng/mL
In adults: 1.6-3/mL

82
Q

what is the daily output of GH in human

A

0.5-1.0mg

83
Q

what cels in the anterior pituitary gland produce Adrenocorticotropic hormone (ACTH, Corticotropin)

A

Corticotropes

84
Q

what percentage do corticotropes constitute in the anterior pituitary

A

20%

85
Q

how many amino acids is ACTH

A

single-chain peptide with 39 amino acids

86
Q

what is the action of ACTH

A

-Stimulates production of glucocorticoids (Cortisol and Corticosterone) and androgens (DHEA Dehydroepiandrosterone and Androstenedione) by the adrenal cortex,
-Maintains size of Zona fasciculate (ie the Glucocorticoids) and Zona reticularis (ie the Androgens) of adrenal cortex

87
Q

WHAT IS THE ACTION OF GH

A

-Stimulates body growth, lipolysis (splitting up/hydrolysis/chemical decomposition of fat),

-inhibits actions of insulin on carbohydrates and lipid metabolism

88
Q

what cells produce thyroid stimulating hormone, thyrotropin

A

Thyrotropes

89
Q

thyrotropes are what percentage of the anterior pituitary gland cells

A

3-5%

90
Q

what is the chemistry of TSH, and thyrotropin

A

Glycoprotein with two subunits;

-α subunit (89)
-β subunit (112)

91
Q

the α subunit of TSH, thyrotropin is has how many amino acids

A

89

92
Q

the β subunit of TSH and thyrotropin has how many amino acids

A

112

93
Q

what is the action of TSH, thyrotropin

A

Stimulates production of thyroid hormones by thyroid follicular cells.

94
Q

is TSH=thyrotropin

A

yes. guy.

95
Q

what cell type produces FSH

A

gonadotropes

96
Q

gonadotropes are what percentage of cells in the anterior pituitary

A

3-5%

97
Q

list all cell types in the anterior pituitary

A

-somatotropes
-gonadotropes
-corticotropes
-thyrotropes
-Lactotropes/mammotropes

98
Q

what is the chemical structure of FSH

A

Glycoprotein with two subunits;
-α (89)
-β subunit (112)

99
Q

the α subunit of FSH has how many amino acids

A

89

100
Q

the β subunit of FSH has how many amino acids

A

112

101
Q

what is the action of FSH

A

-Stimulates development of ovarian follicles
-Regulates spermatogenesis in the testis
-Stimulates estrogen production and secretion by the ovaries.

102
Q

What cell type produces LH

A

gonadotropes

103
Q

what is the chemical structure of LH

A

Glycoprtein with two subunits;
-α subunit (89)
-β subunit (115)

104
Q

how many amino acids does the α subunit of LH have

A

89

105
Q

how many amino acids does the β subunit of LH have

A

115

106
Q

what are the actions of LH

A

-Causes ovulation and formation of the corpus luteum in the ovary
-Stimulates production of estrogens and progesterone by the ovary
-Stimulates testosterone production by the testis (i.e by stimulating interstitial cells of Leydig)

107
Q

what cell types secrete prolactin

A

Lactotropes/Mammotropes

108
Q

what is the chemical structure of prolactin

A

single chain peptide with 198 amino acids

109
Q

what are the actions of prolactin

A

-Stimulates milk secretion and production
-Stimulates mammary growth
-May prevent ovulation in lactating women

110
Q

what hormone does not have a specific target

A

GH, it stimulates all body cells capable of growing

111
Q

functions of GH

A
  1. It stimulates growth generally in the body
  2. It has multiple specific metabolic effects
    -Increases rate of protein synthesis in most cells of the body
    -Increases mobilization of fatty acids from adipose tissue
    -Increases free fatty acids in the blood
    -Increases use of fatty acids for energy
    -Decreases rate of glucose utilization throughout the body
  3. Increase in rate of growth of bone length especially by stimulation of cartilaginous component at the epiphyses and stimulation of osteoblastic cells (as to do with bone-forming) activity causing linear growth
  4. Growth hormone is diabetogenic that is, it can cause elevation of blood sugar level by antagonising the peripheral action of insulin
  5. With thyroxine and cortisol, it assists in milk production
112
Q

list inhibitory and excitatory hormones secreted by the hypothalamus

A
  1. Growth hormone-releasing hormone (GHRH): Stimulates the release of growth hormone
  2. Growth hormone-releasing polypeptide (GHRP): Stimulates the release of GHRH and growth hormone
  3. Growth hormone-inhibitory hormone (GHIH) or somatostatin: Inhibits the growth hormone release
  4. Thyrotropic-releasing hormone (TRH): Stimulates the release of thyroid stimulating hormone
  5. Corticotropin-releasing hormone (CRH): Stimulates the release of adrenocorticotropin
  6. Gonadotropin-releasing hormone (GnRH): Stimulates the release of gonadotropins, FSH and LH
  7. Prolactin-inhibitory hormone (PIH): Inhibits prolactin secretion. It is believed that PIH is dopamine.
113
Q

list the inhibitory hormones from the hypothalamus

A

-Growth hormone-inhibitory hormone (GHIH) or somatostatin: Inhibits the growth hormone release

-Prolactin-inhibitory hormone (PIH): Inhibits prolactin secretion. It is believed that PIH is dopamine.

114
Q

list excitatory hormones of the hypothalamus

A
  1. Growth hormone-releasing hormone (GHRH):
    Stimulates the release of growth hormone
  2. Growth hormone-releasing polypeptide (GHRP):
    Stimulates the release of GHRH and growth hormone
  3. Thyrotropic-releasing hormone (TRH): Stimulates
    the release of thyroid stimulating hormone
  4. Corticotropin-releasing hormone (CRH): Stimulates
    the release of adrenocorticotropin
  5. Gonadotropin-releasing hormone (GnRH): Stimulates the release of gonadotropins, FSH and LH.
115
Q

what is the mechanism of action of GH

A

-Growth hormone causes the liver (and to a lesser extent other tissues) to form several small proteins called somatomedins (MW: 7500) which have the potent effect of increasing all aspects of bone growth.

-Somatomedins is also called insulin-like growth factors (IGFs) because its effects on growth are similar to those of insulin on growth

-Although at least four somatomedins have been identified, the most important is Somatomedin C, also called {Insulin-like- growth factor-I} (IGF-I), with a concentration in plasma that closely follows the rate of growth hormone secretion. Another is IGF-II (insulin-like growth factor-II), which plays an important role in fetus growth.

-Most of the growth effects of growth hormone result from Somatomedin C and other somatomedins, rather than from the direct effects of growth hormone on the bones and other peripheral tissues

116
Q

GH secretion is stimulated by what factors

A
  1. Hypoglycemia
  2. Fasting
  3. Starvation
  4. Exercise
  5. Stress and trauma
  6. Initial stages of sleep
117
Q

GH secretion is inhibited by what factors

A
  1. Hyperglycemia
  2. Increase in free fatty acids in blood
  3. Later stages of sleep
118
Q

how many amino acids is GHRH (Growth Hormone Releasing Hormone)

A

44

119
Q

how many amino acids is GHIH (Growth hormone Inhibitory Hormone) a.k.a somatostatin

A

14

120
Q

what nuclei in the hypothalamus secretes GHRH

A

Ventromedial nucleus, This same area of the hypothalamus is sensitive to blood glucose concentration causing satiety in hyperglycaemic states and hunger in hypoglycaemic states.

121
Q

during prolonged starvation, with depletion of body stores of carbohydrates and proteins

A

50ng/mL

122
Q

what is the role of the hypothalamus in GH secretion

A

Hypothalamus regulates GH secretion via 3
hormones:
1. Growth hormone-releasing hormone (GHRH):
It increases the GH secretion by stimulating the
somatotropes of anterior pituitary
2. Growth hormone-releasing polypeptide (GHRP): It
increases the release of GHRH from hypothalamus
and GH from pituitary
3. Growth hormone-inhibitory hormone (GHIH) or
somatostatin: It decreases the GH secretion.
Somatostatin is also secreted by delta cells of islets
of Langerhans in pancreas.
These 3 hormones are transported from hypothalamus to anterior pituitary by hypothalamo-hypophyseal portal blood vessels.

123
Q

what connects the hypothalamus hormone secretions with the anterior pituitary

A

hypothalamo-hypophyseal portal blood vessels

124
Q

how is GH regulated

A

-Hypothalamus
-Feedback control
-ghrelin

125
Q

Feedback control of GH secretion

A

-GH secretion is under negative feedback control. Hypothalamus releases GHRH and GHRP,
which in turn promote the release of GH from anterior
pituitary. GH acts on various tissues. It also activates
the liver cells to secrete somatomedin C (IGF-I).

-Now, when GH levels are high, somatomedin C stimulates the release of GHIH from hypothalamus.

-GHIH, in turn inhibits the release of GH from pituitary. It acts on pituitary directly and inhibits the secretion of GH.

-Whenever, the blood level of GH decreases again, the GHRH is secreted from the hypothalamus. It in turn causes secretion of GH from pituitary.

126
Q

Regulation of GH by ghrelin

A

Ghrelin is a peptide hormone synthesized by epithelial
cells in the fundus of stomach. It is also produced in
smaller amount in hypothalamus, pituitary, kidney and
placenta. Ghrelin promotes secretion of GH by stimulating somatotropes directly

127
Q

Growth is a complex phenomenon affected by:

A

Growth hormone
Somatomedins
Thyroid hormones
Androgen
Estrogen
Glucocorticoids
Insulin
Genetic factors
Adequate nitrition

128
Q

what happens in the infancy peroid of growth in life?

A

the accelerated growth in infancy is partly due to the continuation of the fetal growth period
- This pattern of growth is episodic or salutatory (dancing or leaping) and not continuous
- Infants increase in length from 0.5-2.5cm in a few days followed by 2-63 days during which no measurable growth can be detected

129
Q

what happens in the late puberty stage of growth in life

A

this growth is due to growth hormone, androgens and estrogens.
- After this period, the is no further increase in height.
- This growth spurt appears earlier in girls because girls mature earlier than boys
- Features of puberty (sequence of events by which a child becomes a young adult):

130
Q

when could be the starting age for puberty in females

A

8

131
Q

when could be the ending age for puberty in females

A

16

132
Q

start of puberty for males

A

10-12

133
Q

end of puberty for males

A

18

134
Q

what is catch-up growth

A

Catch-up growth is a phenomenon where an individual experiences accelerated growth after a period of growth retardation or stunted growth.
This can occur during infancy, childhood, or adolescence, and is usually the result of nutritional deficiencies, chronic illness, or other factors that limit growth.
When the underlying cause of the growth retardation is resolved or improved, the body may undergo catch-up growth to compensate for the lost time. Catch-up growth can help an individual reach their genetically determined height and weight, but it may also be associated with metabolic and hormonal changes that can have long-term health consequences.

135
Q

what is the most important extrinsic factor affecting growth

A

Nutrition

136
Q

what is the role of nutrition on growth

A

Nutrition plays a crucial role in growth, as it provides the necessary nutrients for the multiplication and differentiation of cells, which is essential for growth and development. Adequate intake of macronutrients, such as proteins, carbohydrates, and fats, as well as micronutrients, such as vitamins and minerals, is necessary for optimal growth. For example, proteins are essential for building and repairing tissues, while calcium and vitamin D are necessary for bone growth and mineralization.
Malnutrition, which can result from inadequate intake or absorption of nutrients, can lead to growth retardation, stunted growth, and other developmental abnormalities. Therefore, proper nutrition is critical during infancy, childhood, and adolescence to ensure optimal growth and developmen

137
Q

what hormone is partly responsible for the growth spurt in puberty

A

is due partly to the protein anabolic effect of ANDROGENS (secretion of adrenal androgens increases at this time in both sexes)

138
Q

WHAT hormones terminate growth

A

Estrogens, by causing the epiphyses to fuse to the leg bones (epiphyseal closure), after which linear growth stops

139
Q

what are some disorders caused by hyperactivity of the anterior pituitary

A

Gigantism
Acromegaly
Acromegalic gigantism
Cushing disease

140
Q

what are diseases caused by hypoactivity of the anterior pituitary

A

Dwarfism
Acromicria
Simmond disease

141
Q

what disease is caused by hyperactivity of posterior pituitary

A

Syndrome of inappropriate hypersecretion of ADH (SIADH)

142
Q

what disease is caused by hypoactivity of posterior pituitary

A

Diabetes insipidus

143
Q

what disease is caused by the hypoactivity of both the anterior and posterior pituitary

A

It isn’t necessarily a reduced activity of these 2 glands, but a hyposecretion from the hypothalamus itself. It is called Dystrophia adiposogenitalis

144
Q

why is there no disease that involves hypersecretion of both anterior and posterior pituitary

A

There are no diseases caused by hyperactivity of both the anterior and posterior pituitary because the anterior and posterior pituitary glands are regulated by different mechanisms, and their hormones have different functions.
Hypersecretion of hormones from the anterior and posterior pituitary would result in a complex hormonal imbalance that could cause multiple symptoms and disorders, rather than a single disease.

145
Q

What is gigantism

A

Gigantism is a disorder characterised by abnormally rapid growth. People with the disease are like giants (they range from 7-8ft).
Gigantism is caused by a hypersecretion of GH in childhood(pre-adulthood) before the fusion of the epiphysis of the bone. It is caused by a tumour of the somatotropes (acidophil cells) of the anterior pituitary.
symptoms are:
-Development of a huge stature, height ranges from 7-8ft, limbs are also disproportionately long.
-Giants are hyperglycemic and have glucosuria, and pituitary diabetes. Hyperglycemia overstimulates the b-cells of islets of langerhan to keep producing insulin till they degenerate, and diabetes mellitus develops.
-Tumour of the pituitary gland causes headaches and eventually bitemporal hemianopia, due to a compression of the lateral fibers of the optic chiasma.
-In giants, pan hypopituitarism develops if they remain untreated because the tumour of the pituitary gland grows until the gland itself is destroyed
-The eventual deficiency of pituitary hormone usually causes death in early adulthood

146
Q

what are the symptoms of gigantism

A

-Development of a huge stature, height ranges from 7-8ft, limbs are also disproportionately long.
-Giants are hyperglycemic and have glucosuria, and pituitary diabetes. Hyperglycemia overstimulates the b-cells of islets of langerhan to keep producing insulin till they degenerate, and diabetes mellitus develops.
-Tumour of the pituitary gland causes headaches and eventually bitemporal hemianopia, due to a compression of the lateral fibers of the optic chiasma.
-In giants, pan hypopituitarism develops if they remain untreated because the tumour of the pituitary gland grows until the gland itself is destroyed
-The eventual deficiency of pituitary hormone usually causes death in early adulthood

147
Q

whats the treatment for gigantism

A

surgical removal of the tumour or irradiation of the pituitary gland prevents further gigantism once diagnosed

148
Q

what is acromegaly

A

It is a disorder of the anterior pituitary, characterised by the thickening and broadening of bones, especially in the extremities. It is caused by the overproduction of GH, in adults after the fusion of the epiphysis with the shaft of the bone, caused by a tumour of the somatotropes (acidophils), causing hypersecretion of GH.

149
Q

what are the symptoms of acromegally

A

-Gorilla (acromegallic) face: protrusion of the bony orbit, rough features, broadening of nose, thickening of the lips, thickening and wrinkles on the forehead, prognathism (protrusion of lower jaw).
-Enlargement of hands and feet
-Kyphosis (extreme curvature of upper back –thoracic spine)
-Overgrowth of body hair
-Enlargement of visceral organs such as lungs, thymus, heart, liver and spleen
-Hyperactivity of thyroid, parathyroid and adrenal glands
-Hyperglycemia and glucosuria, resulting in diabetes mellitus
-Hypertension
-Headache
-Visual disturbance (bitemporal hemianopia).

150
Q

what is dwarfism

A

Dwarfism is a pituitary disorder in children, characterized
by the stunted growth. Reduction in GH secretion in infancy or early childhood causes dwarfism.
CAUSES:
-Tumor of the chromophobes: It is a non functioning tumor that compresses and destroys somatotropes.
-Deficiency of GHRH
-Deficiency of somatomedin C
Atrophy or degenration of the somatotropes
-Panhypopituitarism

SYMPTOMS:
-Reproductive function is not affected, if there is
only GH deficiency. However, during panhypopituitarism, the dwarfs do not obtain puberty due to the deficiency of gonadotropic hormones
-A 10yrs old may have the body development of a 4-5yrs old, and at age 20yrs may have the body development of a 7-10yrs old child

TREATMENT: -Human growth hormone can be synthesized by Escherichia Coli bacteria, dwarfs who have pure growth hormone deficiency can be completely cured if treated early in life

151
Q

what are the causes of dwarfism

A

-Tumor of the chromophobes: It is a non functioning tumor that compresses and destroys somatotropes.
-Deficiency of GHRH
-Deficiency of somatomedin C
Atrophy or degenration of the somatotropes
-Panhypopituitarism

152
Q

what are the symptoms of dwarfism

A

-Reproductive function is not affected, if there is
only GH deficiency. However, during panhypopituitarism, the dwarfs do not obtain puberty due to the deficiency of gonadotropic hormones
-A 10yrs old may have the body development of a 4-5yrs old, and at age 20yrs may have the body development of a 7-10yrs old child

153
Q

what is the treatment of dwarfism

A

Human growth hormone can be synthesized by Escherichia Coli bacteria, dwarfs who have pure growth hormone deficiency can be completely cured if treated early in life

154
Q

what bacteria synthesises GH

A

Escherichia Coli bacteria

155
Q

what is pan hypopituitarism

A

-Usually results from
i) 2 tumorous conditions:
-Craniopharyngiomas
-Chromophobe
Craniopharyngiomas and Chromophobe may compress the pituitary gland until the functioning anterior pituitary cells are totally or almost totally destroyed
ii) Thrombosis of the pituitary blood vessels (could occur when a mother develops circulatory shock after the birth of her baby)

-Effects of adult pan hypopituitarism are;
-Hypothyroidism; this a lethargic person (drowsiness), caused by lack of thyroid hormone
-Depressed production of glucocorticoids
-Supressed secretion of the gonadotropic hormone, thus sexual functions are lost
-Gain of weight, (cause of lack of fat mobilization by growth hormone, adrenocorticotropic hormone, adrenocortical hormone and thyroid hormones)

156
Q

how is pan hypopituitarism treated

A

Satisfactory treatment can be obtained by administering adrenocortical and thyroid hormone (except for the abnormal sexual functions)

157
Q

what are the effects of pan hyopituitarism

A

-Hypothyroidism; this a lethargic person (drowsiness), caused by lack of thyroid hormone
-Depressed production of glucocorticoids
-Supressed secretion of the gonadotropic hormone, thus sexual functions are lost
-Gain of weight, (cause of lack of fat mobilization by growth hormone, adrenocorticotropic hormone, adrenocortical hormone and thyroid hormones)

158
Q

what are the causes of hypopituitarism

A

i) 2 tumorous conditions:
-Craniopharyngiomas
-Chromophobe
Craniopharyngiomas and Chromophobe may compress the pituitary gland until the functioning anterior pituitary cells are totally or almost totally destroyed

ii) Thrombosis of the pituitary blood vessels (could occur when a mother develops circulatory shock after the birth of her baby)

159
Q
A
160
Q

a

A

MB prep: Physiology (12 decks)

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