Endocrine System

Question 1

What is the endocrine system?

Answer 1

A collection of ductless glands, which produce hormones and deliver them into the bloodstream, lymph or tissue fluid.

Question 2

Define tropic

Answer 2

-Released by an endocrine gland and act upon another endocrine gland

Question 3

Define trophic

Answer 3

-hormones stimulate growth in target tissues.
-may lead to hypertrophy.

Question 4

What must a hormone have to affect a specific target organ?

Answer 4

Target cells must have receptors that respond to the signal (hormone).

-also important that other organs which are not the target do not respond to the hormone, so they lack receptors.

Question 5

What are hormones?

Answer 5

Molecular triggers

Question 6

Name endocrine organs

Answer 6

-pituitary gland
-pineal gland
-thyroid gland
-parathyroid glands
-adrenal glands (x2)

Question 7

Name endocrine cells in other organs

Answer 7

-pancreas
-gonads
-hypothalamus

Question 8

What are the hormone classifications?

Answer 8

Steroid hormones - lipid molecules derived from cholesterol (e.g ;oestrogen, testosterone)

Protein hormones - polypeptide chains containing multiple amino acids (e.g FSH, insulin)

Amine hormones - derived from the amino acids tyrosine and tryptophan = modified amino acids (e.g ; epinephrine , norepinephrine)

Question 9

How are hormones secreted in response to stimuli ?

Answer 9

Changing levels of chemicals in the blood: known as humoral stimuli, endocrine gland responds to extracellular environment (increase in blood glucose levels = stimulates release of insulin from pancreas).

Nerve impulses: known as neural stimuli, release of hormones is stimulated by nerves.

Hormones: known as hormonal stimuli, trophic hormone acts on endocrine gland to release hormone

Question 10

Based on the effect the hormone has on the target cells, hormones are classified in two categories:

Answer 10

1. Those that act via appropriate receptors on the cell surface and use a second messenger- known as signal transduction (protein hormones)
2. Those that penetrate into the cell and exert their effect directly on the cell nucleus and cellular protein synthesis - known as direct Intracellular stimulation (likely to be steroidal hormones)

Question 11

Signal transduction

Answer 11

Hormone in the blood (classed as first messenger) binds with specific receptor protein on plasma membrane of the target cell.
- generates a chemical signal within the cell by activating a series of intracellular molecules called a second messenger .
- the second messenger then acts on the target cell, influencing protein synthesis and hormone secretion.

Examples of 2nd messengers inc - cyclic AMP (cAMP), protein kinases, phosphates, calcium ions (Ca2+), nitric oxide (NO).

Question 12

How do peptide hormones exert their effect ?

Answer 12

Signal transduction.

Question 13

peptide hormones are:

Answer 13

-hydrophilic (water loving)
-lipophobic (fat hating)

This means they cannot pass through the lipid belayer of the cell membrane.

E.g - insulin, glucagon, leptin, oxytocin

Question 14

What is direct intracellular stimulation ?

Answer 14

• hormone crosses the lipid membrane of target cell

-it binds it receptors in either cytoplasm or nucleus forming an active receptor-hormone complex

-this complex moves into the nucleus and binds directly to DNA.

-influences gene expression and the action of the cell.

Question 15

How do steroid hormones exert their effect ?

Answer 15

Direct intracellular stimulation

Question 16

About steroid hormones:

Answer 16

-lipophilic (fat loving).
Can diffuse across lipid bilayer of the cell.

E.g - oestrogen, progesterone, testosterone

Question 17

What are feedback mechanisms

Answer 17

-prevent/enhance excessive secretion of hormones once an effect has been achieved.

Question 18

How does the brain aid the endocrine system ?

Answer 18

• through its effect on the pituitary gland.

-constant interaction between the endocrine organs and the CNS.
(Brain controls endocrine function)
(Hormones effect function of the CNS)

Question 19

How does the hypothalamus control the pituitary?

Answer 19

Either

-via portal circulation (special blood vessels) to the anterior pituitary.

Or

Neural connects to the posterior pituitary.

Question 20

View notebook for hormone tables

Question 21

Where is the pineal gland located?

Answer 21

Between the 2 cerebral hemispheres

Question 22

What is the function of the pineal gland ?

Answer 22

• produces hormone melatonin
  (More is produced when dark vs daylight)

-involved in managing the circadian rhythm/seasonal breeders.
(Melatonin inhibits secretion of FSH and LH by inhibiting release of GnRH from hypothalamus).

Question 23

Where is the thyroid gland located?

Answer 23

• 2 lobes near the larynx

-One lobe each side of trachea
(May or may not have isthmus)

Question 24

What is the function of the thyroid gland ?

Answer 24

-produces 2 hormones in response to TSH from anterior pituitary;
Thyroid hormone (metabolic rate)
Calcitonin (calcium absorption)

Question 25

Where are the parathyroid glands located ?

Answer 25

-small nodes located within or near the thyroid gland.

(Usually 2 either side of the thyroid gland - species variations).

Question 26

What is the function of the parathyroid glands ?

Answer 26

Secrete parathyroid hormone (parathormone)
= Ca release from bones

Question 27

Where are the adrenal glands located ?

Answer 27

-located close to the kidneys
(Shape, size and location vary with species)

Question 28

What is the function of the adrenal glands ?

Answer 28

-pair of glands, consisting of an outer cortex and inner medulla

Adrenal cortex = secretes lipid based steroid hormones corticosteroids.

Adrenal medulla = neural origin (sympathetic nervous system) norepinephrine (noradrenalin) & epinephrine (Adrenalin)

Question 29

Where is the pancreas located ?

Answer 29

• located near to/adjacent to the duodenum

Question 30

About the pancreas

Answer 30

-has both exocrine and endocrine cells (mixed gland)

-endocrine cells known as islets of Langerhans - there are 3 types of islet cell (alpha, beta, gamma)

-alpha cells = produce hormone glucagon - increases blood glucose level

-beta cells = (most common) produce hormone insulin - decrease blood glucose levels

-gamma cells = (rare) produce hormone somatostatin; mild modifying effect on insulin and glucagon.

Question 31

What is the function of the testes ?

Answer 31

• secrete testosterone plus small amount of oestrogen.

-cells of Leydig secrete testosterone stimulated by LH

-testosterone is responsible for :
O Development of male characteristics
O Male behaviours patterns - aggression, territorial behaviour, sex drive, courtship behaviour
O Development of spermatozoa

Question 32

What is the function of the ovaries ?

Answer 32

• secrete oestrogen and progesterone

O Stimulated by FSH and LH secreted from the anterior pituitary gland.

O FSH secretion inhibited by oestrogen (gives positive feedback) and progesterone via negative feedback loops.

O LH secretion inhibited by progesterone from corpus luteum via negative feedback loop.

O Ripening follicles in ovaries secrete oestrogen.

O Corpus luteum secrete progesterone and some oestrogen.

Question 33

What is oestrogen responsible for ?

Answer 33

• female behaviour associated with oestrus

-preparing the reproductive tract for mating (increased secretions to facilitate mating).

-negative feedback on the anterior pituitary gland = inhibits further secretion of FSH from pituitary.

Question 34

What is progesterone responsible for?

Answer 34

• preparing the reproductive tract for pregnancy and maintaining pregnancy.

-inhibits secretion of luteinising hormone (LH) from anterior pituitary gland.

-Inhibits further secretion of FSH.