Lecture 27: Endocrine glands Flashcards Preview

1060 Human form and function > Lecture 27: Endocrine glands > Flashcards

Flashcards in Lecture 27: Endocrine glands Deck (41):
1

What are hormones??

Chemical signalling system, complementary to the nervous system

Resemble neurotransmitters

 

But:
Hormones – widespread action

Neurotransmitters – local 

2

big difference between hormones and neurotransmitters??

Hormones – widespread action 

they are realeased into the blood and work on all the receptors that can bind with them

Neurotransmitters – local 

They are released into synapses

3

Difference between exocrine and endocrine glands??

Exocrine glands: body surface

Endocrine glands: hormones, via blood 

 

Exocrine glands are glands that produce and secrete substances onto an epithelial surface by way of a duct. Examples of exocrine glands include sweat, salivary, mammary, ceruminous, lacrimal, sebaceous, and mucous.

-

Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus and adrenal glands.

 

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4

what are the classes of hormones ??

Amino acid derivatives e.g. adrenaline

Small peptides e.g. ADH
Proteins e.g. Growth hormone, insulin

Steroids e.g. cortisol, oestrogen 

5

Characteristics of hormone secreting cells??

(Peptide/protein hormone cell)

Peptide/protein hormone cell

– Lots of rER
– Golgi
– Secretory vesicles 

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6

Characteristics of hormone secreting cells?? 

(Steroid-secreting cells )

Steroid-secreting cells

– Lots of smooth ER
– Abundant mitochondria

– Lipid droplets 

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7

Pituitary Gland ??

(Hypophysis cerebri)

Major interface between brain and the endocrine system. 

8

Anatomy of the pituitary ??

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rounded body, about 1 cm dia.

connected to floor of III ventricle by the infundibulum (pituitary stalk), just posterior to the optic chiasma 

 

lies in a depression in the body of the sphenoid 

pituitary (hypophyseal) fossa

also called the sella turcica 

 

Pituitary fossa is lined by dura and covered over by a sheet of dura (diaphragma sellae), pierced by the pituitary stalk 

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9

The pituitary has 2 distinct parts. 

what are they ??

Adenohypophysis (Anterior pituitary)  (green part)

- pars distalis
- pars tuberalis
- pars intermedia 

Neurohypophysis (Posterior pituitary) (grey part)

- pars nervosa

- infundibulum (neural stalk) 

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10

The pituitary has 2 distinct parts with different origins.

what are the origins??

Adenohypophysis

- an upgrowth of ectoderm/endoderm from the embryonic oral cavity (Rathke’s Pouch).

Neurohypophysis

- downgrowth from floor of the diencephalon. 

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11

Posterior pituitary ??

Consists of axons of modified neurones, supported by a population of glial-like cells, called pituicytes.

Cell bodies of these neurones lie in the supraoptic and paraventricular nuclei of the hypothalamus. 

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12

what does ADH do?

antidiuretic hormone (ADH, vasopressin)

increases water retention in kidney.

raises blood pressure by contracting vascular smooth muscle cells (at high concentrations). 

13

which transmitters are secreted from the pituitary?

“Transmitters” are the hormones: 

antidiuretic hormone (ADH, vasopressin)

increases water retention in kidney.

raises blood pressure by contracting vascular smooth muscle cells (at high concentrations).

oxytocin

contraction of smooth muscle cells, esp. of uterus during childbirth; and myoepithelial cells of mammary gland during lactation. 

14

what does oxytosin do ??

oxytocin

contraction of smooth muscle cells, esp. of uterus during childbirth; and myoepithelial cells of mammary gland during lactation. 

 

may also be involved in enchancing trust between individuals.

15

ADH and oxytocin are ??

where are they made

ADH and oxytocin are peptides (9 aa each, 2 different)

made in cell bodies of neurones (in hypothalamus) as a larger protein, subsequently cleaved to yield the hormone and a binding protein (neurophysin).

transported down axons to terminals

released from terminals into fenestrated capillaries on stimulation of the cell bodies in the hypothalamus.

accumulations of hormone within the axons exist, called Herring bodies 

16

Anterior pituitary ??

Pars distalis

Cords of cuboidal/polygonal epithelial secretory cells clustered around large, fenestrated sinusoids.

Traditionally classified into:

– Acidophils

– Basophils
– Chromophobes 

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17

which hormones do the acidophils in the anterior pituitary secrete??

Acidophils:
Somatotrophs  - growth hormone

Mammotrophs - prolactin

18

which hormones do the basophils in the anterior pituitary secrete??

Basophils:
Thyrotrophs - Thyroid Stim. Hormone 
Corticotrophs - Adrenocorticotrophic hormone 

Gonadotrophs -  Follicle stim. Hormone and Luteinizing hormone 

19

what the role of the chromophobes in the anterior pituitary??

Chromophobes 

either reserve cells or resting cells that have lost their secretory granules 

not sure what their role is

20

cell structure in the Pars tuberalis ??

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Thin layer of cuboidal cells, mostly gonadotrophs. 

21

role of Pars intermedia ??

Cells secrete Melanocyte stimulating hormone

– increases skin pigmentation, but physiological role in man is uncertain. 

22

Anterior pituitary regulation of secretion ?

Anterior pituitary is regulated by neuroendocrine cells of the hypothalamus whose axons project to the median eminence.

– discharge into capillaries of the pituitary portal vessels.

– these in turn end in capillaries bathing the cells of the anterior pituitary. 

 

The hypothalamic hormones either stimulate or inhibit the release of hormones from the anterior pituitary.

e.g.

Thyrotropin releasing hormone (TRH)

Gonadotropin releasing hormone (GnRH)

Growth hormone releasing hormone (GRH)

Corticotropin releasing hormone (CRH)

Somatostatin (blocks GH and TSH release)

Dopamine (blocks prolactin release) 

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23

Why have a portal system? 

1. Need less releasing hormone

2. More immediate response

3. Can use the same hormone again elsewhere for other purposes

e.g. somatostatin from Islets of Langerhans blocks release of insulin and glucagon. 

24

Anatomy of the thyroid gland??

2 pear-shaped lateral lobes connected by a midline isthmus

intimately related to the trachea

isthmus lies at level of 2nd-4th tracheal rings

isthmus may be joined to the hyoid bone by a fibrous cord, a remnant of the embryological thyroglossal duct 

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25

Development of the thyroid??

Arises from a diverticulum in floor of the primitive pharynx just caudal to the site of the future tongue

– thyroglossal duct
– opens at base of tongue as the foramen caecum

– connection to pharynx eventually lost, isolating the gland 

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26

Cellular organization of the thyroid gland??

Thyroid epithelial cells are organized into follicles.

–  secrete thyroglobulin
(large glycoprotein, mw 660Kd)

–  accumulates in the follicles as “colloid” 

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27

explain

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Thyroid follicular cells take up iodide

–  oxidized to Iodine

–  covalently attached to the tyrosines of thyroglobulin within the lumen of the follicle

On stimulation by TSH (from the anterior pituitary)

–  follicular cells endocytose the iodinated thyroglobulin

–  break it down in lysosomes

–  release the iodinated tyrosine derivatives as tetra- iodothyronine (thyroxine) (T4) or tri-iodothyronine (T3) 

28

C cells/Parafollicular cells in the thyroid gland??

scattered cells found within the follicular epithelium or as clusters between the follicles.

larger, more rounded than the follicle cells

secrete calcitonin (inhibits Ca++ mobilization)

neural crest-derived - migrate to thyroid during development. 

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29

Anatomy of the parathyroid glands??

2 pairs of parathyroid glands, each about the size of a pea

Usually found on or embedded in the posterior border of the lateral lobes of the thyroid gland, but position is somewhat variable (esp. inferior parathyroids)

No functional significance in the association between thyroid and parathyroid glands 

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30

Cellular organization of the parathyroid glands??

Densely-packed, small Chief (or principal) cells arranged in irregular cords around blood vessels.

–  secrete parathyroid hormone (parathormone)

–  stimulates calcium mobilization. 

 

There is a second, minor population of larger, eosinophilic oxyphil cells, of unknown function

(lack secretory granules). 

31

Anatomy of the Adrenal (suprarenal) Gland ??

Pyramidal (right) or crescent-shaped (left) bodies in contact with the upper poles of the kidneys

Separated from kidneys by connective tissue but surrounded by the renal fascia. 

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32

Development of the adrenal glands??

he adrenal glands have 2 distinct parts with different origins:

Cortex
– derived from the coelomic epithelium (mesothelium)

lining the posterior abdominal wall

Medulla
– derived from an adjacent sympathetic ganglion 

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33

structure and function of the adrenal cortex??

Cells secrete steroids

have lots of SER and lipid droplets (containing cholesterol) so appear pale and "frothy" in histological sections.

Cells are organized into 3 zones:-

Zona glomerulosa

Zona fasciculata

Zona reticularis 

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34

what is the cell arrangement and function of zona glomerulosa in the adrenal cortex?

cells arranged in rounded clusters, surrounded by capillaries

 secrete mineralocorticoids – mainly aldosterone (95%)

Target : Na+ retention in kidney

– (distal convoluted tubule)

regulated by renin/anigiotensin system 

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35

what is the cell arrangement and function of zona fasciculata in the adrenal cortex?

cells arranged in straight cords, running radially

secrete glucocorticoids – mainly cortisol (95%)

Target : glucose, lipid and protein metabolism

secretion regulated by ACTH 

36

what is the cell arrangement and function of zona reticularis in the adrenal cortex?

cells arranged in irregular cords

secrete some glucocorticoids and small quantities of sex steroids (mostly weak androgens)

functionally insignificant (?) 

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37

Adrenal Medulla structure??

modified sympathetic ganglion

large, polyhedral cells arranged in clumps or cords

resemble “axon-less” ganglion cells 

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38

function of the adrenal medulla?

receive a (cholinergic) preganglionic sympathetic input from the greater and lesser splanchnic nerves, via the coeliac ganglion.

on stimulation, secrete catecholamines directly into the blood

80% of the cells secrete adrenaline (epinephrine); the rest, noradrenalin (norepinephrine) 

 

The high concentration of glucocorticoids from the cortex is needed to induce the enzyme responsible for converting noradrenalin to adrenalin. 

 

cells stain when treated with chromate salts due to reaction with catecholamines

– often referred to as chromaffin cells 

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39

Islets of Langerhans ??

Small, rounded clusters of cells, 100-200 μm dia., embedded within the exocrine pancreas

The cells are smaller and more-lightly stained than the exocrine cells, and arranged in irregular cords around capillaries. 

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40

Using immunocytochemistry, 4 main cell types can be distinguished in the islets of Langerhans 

what are they and what do they secrete?

A or alpha cells (~20%) secrete glucagon

B or beta cells (~70%) secrete insulin

D or delta cells (5-10%) secrete somatostatin

F or PP cells (1-2%) secrete pancreatic polypeptide

Other, minor cell types secrete vasoactive- intestinal peptide (VIP), substance P, motilin, serotonin, etc. 

41

Diffuse neuroendocrine system ??

Scattered cells found especially in the gut and respiratory system

Secrete amines or peptides with hormone-like or neurotransmitter activity

e.g. gastrin, CCK, secretin, enteroglucagon, serotonin etc

Oftensecretelocally (paracrine) 

 

Cells often have ability to take up and decarboxylate amines

– Old name – APUD cells (amine precursor uptake and decarboxylation)

Possess synaptic vesicle-like structures or neurosecretory- type granules (dense core granules)

– released by exocytosis in response to external stimuli