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24-25 HUMAN PHYSIOLOGY > The Endocrine System > Flashcards

The Endocrine System Flashcards

1
Q

Definition of a Hormone

A

chemical that transfers information and instructions between cells in animals

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2
Q

What do hormones regulate?

A
  • Growth and development
  • Control the function of various tissues
  • Support reproductive function
  • Regulate metabolism (break down food to create energy)
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3
Q

Four types of hormone delivery

A

AUTOCRINE

  • Feeds-back on the same cell
  • Without entering blood circulation

PARACRINE

  • Diffuses to its adjacent target cells
  • Via immediate extracellular space
  • Blood not directly involved

ENDOCRINE

  • Delivered to target cells by blood circulation

NEUROENDOCRINE:

  • Produced and released by a neuron
  • Delivered to target cells by bloodstream
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4
Q

Four mechanisms of intercellular communication

A

DIRECT COMM

  • Via gap junctions
  • Involves ions, solutes, lipid-soluble materials
  • Limited to adjacent cells of the same type

PARACRINE COMM

  • Via extracellular fluid
  • Involves paracrine factors
  • Limited to a local area

ENDOCRINE COMM

  • Via bloodstream
  • Involves hormones
  • Limited to tissues and organs with appropriate receptors

SYNAPTIC COMM

  • Across synapses
  • Involves neurotransmitter
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5
Q

Hypothalamus

A
  • Produces regulatory hormones (pituitary gland)
  • Produces ADH, OXT
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6
Q

Thyroid

A
  • Location: Below the larynx
  • Produces triiodothyronine (T3) and thyroxine (T4)
    • Sets the basal metabolism rate
    • Regulates body temperature
    • Growth and development
  • Calcitonin (CT)
    • Decreases calcium levels (store in bones)
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7
Q

Adrenal Glands

A
  • Medulla
    • Epinepherine
    • Norepinephrine
  • Cortex
    • Cortisol
    • Corticosterone
    • Aldosterone
    • Androgens
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8
Q

Pancreatic Islets

A

Alpha cells

  • Secrete glucagon
  • In response to low blood glucose
  • Stimulates glycogenolysis and lipolysis

Beta cells

  • Secrete insulin
  • In response to high blood glucose
  • Promotes entry of glucose into cells
  • Promotes conversion of glucose into glycogen and fat
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9
Q

Pineal gland

A
  • Location: Basal forebrain near thalamus
  • Secretes melatonin
  • In response to suprachiasmatic nucleus (SCN) of hypothalamus
  • Regulates circadian rhythms
  • Secreted at night and inhibited by light
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10
Q

Parathyroid gland

A
  • 4 glands embedded in lateral lobes of post. side of thyroid gland
  • Secrete Parathyroid hormone (PTH)
  • Stimulates osteoclasts (break down bone) and inhibits osteoblasts (form new bone)
    • ↑ osteoclasts releases Ca2+ from bone
    • ↓ osteoblasts reduces rate of Ca2+ deposition in bone
  • Enhances reabsorption of Ca2+ at kidneys
  • Stimulates formation and secretion of calcitriol by the kidneys
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11
Q

Six organs with secondary endocrine function

A

HEART

  • ANP and BNP
    • Decrease cardiac output
    • Lowers blood pressure

THYMUS

  • Thymosins (atrophy during adulthood)
    • Promotes T cell maturation

ADIPOSE TISSUE

  • Leptin
    • Prevent overeating

DIGESTIVE TRACT

  • Ghrelin by stomach
    • Stimulates hunger
  • CCK by small intestine
    • Stimulates bile release

KIDNEYS

  • Erythropoetin (EPO)
    • Stimulates production of RBC
  • Calcitriol
    • Increases calcium levels

GONADS

  • Testes: testosterone, inhibin
  • Ovaries: estrogen, progesterone, inhibin
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12
Q

Three chemical classifications of hormones

A
  • Amino acid tyrosine
    • Secreted by thyroid (T3, T4, CT)
    • Or adrenal medulla (Epinepherine, norepinepherin)
  • Proteins and Peptides
    • Anterior and posterior pituitary glands
    • Pancreas (insulin, glucagon)
    • Parathyroid gland
  • Steroids
    • Adrenal cortex (cortisol, aldosterone)
    • Ovaries, testes, and placenta
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13
Q

Prohormones and prehormones

A
  • Prohormones are precursors of hormones, e.g. proinsulin
  • Prehormones are precursors of prohormones, e.g. preinsulin
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14
Q

Nervous system VS Endocrine system

A

NERVOUS SYSTEM

  • “Wired” with structural arrangement
  • Releases neurotransmitters into synaptic cleft
  • Short distance
  • Rapid response
  • Brief duration of action (eg reflexes)

ENDOCRINE SYSTEM

  • “Wireless” system
  • Releases hormones into bloodstream
  • Long distance
  • Slow response
  • Long duration of action
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15
Q

Two mechanisms of hormone action

A

HYDROPHOBIC (Steroid) hormones

  • Receptors in target’s cytoplasm or nucleus
  • Can diffuse thru plasma membrane
  • Targets nucleus to affect transcription
  • Genomic action
  • Takes at least 30 mins

HYDROPHILIC (Peptide) hormones

  • Receptors on surface of target cell
  • Act through 2nd messengers
  • Quick effects
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16
Q

Describe the bind to nuclear hormone receptors for hydrophobic hormone action

A
  • Travel in blood attached to carrier proteins
  • Dissociate from carriers to pass thru plasma membrane
  • Bind to nuclear hormone receptors in the cell
  • Serve as transcription factors to activate transcription
  • Superfamily: Steroid family and thyroid hormone
17
Q

Describe the adenylate cyclase-cAMP second messenger system in hydrophilic hormones

A

1) Hormone binds to receptor
2) Activates G-protein
3) Activates adenylate cyclase
4) Enzyme converts ATP into cAMP
4) cAMP activates protein kinase A
5) PKA phosphorylates enzymes that produce
hormone’s effects
6) cAMP inactivated by phosphodiesterase

Adrenaline binding to beta receptors

18
Q

Describe the phospholipase-C-Ca2+ second messenger system in hydrophilic hormones

A

1) Hormone binds to receptor
2) Activates G-protein
3) Activates phospholipase C
4) Phospholipase C splits phospholipid into 2nd messengers IP3 and DAG
5) IP3 binds on endoplasmic reticulum receptors
6) Ca2+ channels open
7) Calcium released into the cytoplasm
8) Activates calmodulin
9) Activates protein kinase C
10) PKC adds phosphates to proteins altering enzyme activity
e.g. glycogen → glucose-1-phosphate → glucose 6 phosphate → glucose → blood

Adrenaline binding to alpha receptors

19
Q

Describe the tyrosine kinase second messenger system in insulin

A

1) Insulin binds to receptor
2) Receptor = enzyme called tyrosine kinase
3) Alpha subunit of receptor sticks out on extracellular side, beta subunit embedded within plasma membrane
4) Insulin binds to alpha subunit of receptor
5) Two receptor units come together (dimerization)
6) Beta subunits phosphorylate eo
7) Activated tyrosine kinase phosphorylates other molecules
e.g. signals molecules to induce hormone/growth factor effects

20
Q

The six hormones produced by the anterior pituitary gland

A

Produces own hormones controlled by the hypothalamus

  • Growth hormone promotes growth, protein synthesis, and movement of amino acids into cells
  • Thyroid stimulating hormone stimulates thyroid to produce and secrete T4 and T3
  • Adrenocorticotropic hormone stimulates adrenal cortex to secrete cortisol
  • Follicle stimulating hormone stimulates growth of ovarian follicles and sperm production
  • Luteinizing hormone causes ovulation and secretion of testosterone in testes
  • Prolactin stimulates milk production by mammary glands
21
Q

Cortisol pathway

A
  1. Hypothalamus releases corticotrophin-releasing hormone (CRH)
  2. Stimulates anterior pituitary to produce adrenocorticotropic hormone (ACTH)
  3. Stimulates adrenal cortex to release cortisol
22
Q

What is cortisol?

A
  • Steroid hormone
  • Regulates circadian rhythm
  • 80% carried in blood by cortico-steroid binding globulin
  • 15% bound to albumin
  • 5% free in solution
  • Main function
    • Proteins broken down to amino acid
    • Amino acid converted to glucose
    • Nitrogen produced as by-product, excreted as urea
    • Increases blood glucose
23
Q

Describe the hypothalamic control of the posterior pituitary

A
  • Hormones transported along hypothalamo-hypophyseal tract to posterior pituitary
  • Release controlled in hypothalamus by neuroendocrine reflexes

ADH

  • Supraoptic nuclei of hypothalamus produces ADH
  • Promotes H2O conservation by kidneys

Oxytocin

  • Paraventricular nuclei of hypothalamus produces oxytocin
  • Stimulates contractions of uterus during parturition
  • Stimulates contractions of mammary gland alveoli for milk-ejection reflex
24
Q

The two classes of hypothalamic regulatory hormones in the anterior lobe

A

Releasing hormones (RH)

  • Stimulate synthesis and secretion of hormones at anterior lobe

Inhibiting hormones (IH)

  • Prevent synthesis and secretion of hormones
  • Rate of secretion is controlled by negative
    feedback

Both hormones are…

  • Released from axon endings into capillary bed in median eminence
  • Carried by hypothalamo-hypophyseal portal system
  • Reaches anterior lobe to regulate secretion of hormones
25
Q

Feedback control of the anterior pituitary

A

Hypothalamic-pituitary gonad axis (control system)

  • eg inhibits secretion of GnRH
  • Short feedback loop (retrogade flow of blood)
  • Negative feedback of target gland hormones
  • Positive feedback during menstrual cycle
    • Estrogen stimulates “LH surge”
26
Q

Describe the adrenal glands

A

Location: Lie along superior border of each kidney

  • Superficial adrenal cortex
    • Stores lipids (cholesterol, fatty acids)
    • Manufactures steroid hormones (corticosteroids, cortisol, aldosterone)
  • Inner adrenal medulla
    • Controlled by sympathetic division
    • Produces epinephrine and norepinephrine
    • Metabolic changes last several minutes
27
Q

Inner adrenal medulla

A
  • Synthesizes and secretes 80% pinephrine and 20% norepinephrine
  • Hormonal effects of epinephrine last 10X longer than norepinephrine
  • Innervated by direct preganglionic sympathetic fibers
  • Activated during “fight or flight” response
    • Increased respiratory rate
    • Increased HR and cardiac output
    • General vasoconstriction increasing venous return
    • Vasodilation towards skeletal muscle
    • Glycogenolysis and lipolysis
28
Q

Superficial adrenal cortex

A
  • Cortex is controlled by adrenocorticotrophic hormone (ACTH)
  • Secretes
    • Aldosterone: Stimulate kidneys to reabsorb Na+ and secrete K+
    • Cortisol: Inhibits glucose utilization and stimulates gluconeogenesis
    • Supplementary sex steroids
29
Q

Layers of the adrenal gland

A
  • Adrenal capsule
  • Zona glomerulosa (aldosterone stimulated by angiotensin II)
  • Zona fasciculata (cortisol stimulated by ACTH)
  • Zona reticularis (androgens stimulated by ACTH)
  • Adrenal medulla (adrenaline stimulated by sympathetic nerve)
30
Q

Functions of the thyroid hormones

A
  • Calorigenesis (heat production)
  • ↑ oxygen consumption
  • ↑ cardiac output
  • ↑ breathing rate
  • ↑ no. of RBC
  • ↑ carbohydrate metabolism
  • ↑ lipid metabolism
  • ↑ protein metabolism
  • Skeletal growth, teeth, hair follicles and skin
  • Mental alertness
31
Q

Hypothyroidism

A
  • Insufficient thyroid hormones
  • Low BMR, weight gain, lethargy, cold intolerance
  • Myxedema = puffy face, hands, feet
  • Cretinism (severe mental retardation)
32
Q

Hyperthyroidism

A
  • Goiter (enlarged thyroid gland)
  • Grave disease = Autoimmune disease where antibodies act like TSH
  • Exopthalmos (eyes protruding)
    • Immune attacks soft tissue around eyes
    • Fatty tissue and muscles enlarge
  • High BMR, weight loss, heat intolerance

24-25 HUMAN PHYSIOLOGY (11 decks)

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