The Endocrine System

Question 1

What is the function of the endocrine system?

Answer 1

Regulation and control of various functions that are performed through chemicals (hormones)

Question 2

What are hormones released by?

Answer 2

endocrine glands

Question 3

What is endocrinology?

Answer 3

study of endocrine glands and their secretions

Question 4

What is a hormone?

Answer 4

bioactive messenger molecule secreted by endocrine glands into the blood

rapidly destroyed so that a new message can be sent

Question 5

What is an endocrine gland?

Answer 5

ductless gland

hormone producing cells that secrete hormones into the bloodstream

chemicals circulate through the whole body eg; adrenal glands

Question 6

What is an exocrine gland?

Answer 6

secretions released outside the body into the GI tract

always have a duct (opening)

gland products are localised to a region around the duct eg; sweat glands

Question 7

What are the functions under the control of the endocrine system?

Answer 7

digestion related metabolic processes

osmoregulation, excretion

growth and morphological changes

reproductive organs

Question 8

What does endocrine and paracrine mean in relation to hormones?

Answer 8

ENDOCRINE: circulate in/ throughout the body

PARACRINE: local hormone receptor

only the organs that have the specific receptors can respond to the hormone

Question 9

What might stimulate secretion of a hormone?

Answer 9

Nerve impulses
Releasing hormone
Levels of chemicals in blood
Feedback loops

Question 10

What is the role of feedback loops?

Answer 10

prevent over secretion or reduce secretion once the effect has been achieved

Question 11

What are the three distinctive groups of hormones? give examples.

Answer 11

1. Tyrosine Derived
   - Adrenaline
   - Thyroxin
   - Triiodothyronine
2. Steroids
   - Testosterone
   - Oestrogen
   - Progesterone
   - Corticosteroids
3. Peptides and Proteins
   - Hormones
   - Insulin
   - Glucagon
   - Gastrin
   - Large proteins
   - Growth hormone
   - Prolactin
   - FSH/LH

Question 12

What are the 4 endocrine glands in the dog?

Answer 12

pancreas
adrenal
thyroid 
parathyroid
pituitary
hypothalamus

Question 13

What are all the glands?

Answer 13

pancreas
adrenal
thyroid 
pituitary 
parathyroid
ovaries
testes

Question 14

What is the hypothalamus?

Answer 14

the control centre in the centre of the brain

interface (nervous and endocrine functions)

Question 15

What is the HYPOTHALAMON-PITUITARY AXIS?

Answer 15

The hypothalamus receives info from the nervous system
Responds by releasing hormones
They set off a chain reaction of hormones from other glands
This is called a cascade

Question 16

What is a cascade?

Answer 16

The hypothalamus receives info from the nervous system
Responds by releasing hormones
They set off a chain reaction of hormones from other glands

Question 17

What is the pituitary gland?

Answer 17

pea sized gland
connected to hypothalamus by a stalk
most releasing hormones from the hypothalamus act on the pituitary
the pituitary then releases hormones that act on other glands and tissues

Question 18

What is the posterior pituitary?

Answer 18

Neurohypophysis

extension of hypothalamus that is composed of axons of hypothalamic neurones which extend downward as a large bundle behind the anterior pituitary

posterior grows down from the hypothalamus and is full of nerve endings

Question 19

How does the hypothalamus work?

Answer 19

senses need for anterior pituitary hormones
forms posterior pituitary hormones
integration of autonomic nervous system function

Question 20

In Posterior lobe secretions, what two hormones re released into the capillary bed?

Answer 20

ADH- acts on the walls of the distal kidney tubules to control water and solute levels

Oxytocin- triggers uterine muscle contraction at parturition and acts on mammary glands to release milk

Question 21

What is the anterior also known as?

Answer 21

Anterior- Aden-hypophysis
classical gland that is connected to the hypothalamus by capillaries.
Plexus- blood vessels
The direct blood connection is important because blood speeds up the information being passed on

Question 22

What hormones is the anterior pituitary responsible for?

Answer 22

• Growth hormone: critical role in all cellular growth- regulates production of proteins by cells; controlled by GH releasing hormone in hypothalamus. Overproduction – gigantism; underproduction – dwarfism
• Thyrotropin or TSH: regulated by Thyrotopin releasing hormone TRH - stimulates thyroid to produce T4, T3 and calcitonin
• ACTH (Adrenocorticotropic hormone): regulated by CTH from hypothalamus –regulates production of glucocorticoids ( cortisol and corticosterone) from adrenal cortex
• Follicle stimulating hormone (FSH) secreted in response to production of gonadotrophin releasing hormone- FSH acts on ovarian follicles – promotes spermatogenesis
• Leuteinising hormone (LH) stimulates ovulation and development of corpus leuteum – regulates testosterone production
• Prolactin: stimulates mammary glands to produce milk

Question 23

What does the thyroid gland produce?

Answer 23

THYROXINE (T4) AND TRI-IODOTHYRONINE (T3)
Influence metabolic rates, growth and development
(Hyperthyroidism in cats and hypothyroidism in dogs)

CALCITONIN
reduces blood Ca ion concentration which inhibits osteoclast activity and regulates bone growth in young animals

Question 24

What are parathyroid glands and where are they situated?

Answer 24

Situated close to the thyroid
Chief cells secrete parathormone
Secretion is dependant on the levels of Ca in the blood.

Question 25

What is the function of Parathyroid glands?

Answer 25

• Function – increases circulating Ca: • Stimulates osteoclasts causing a breakdown of bone matrix • Inhibits osteoblasts • Absorption of Ca from the intestine is increased • Stimulates reabsorption of Ca by kidney • Works with calcitonin – maintain homeostasis • Deficiency – hypocalcaemia – tetany • Over secretion hyperparathyroidism

Question 26

What are the cells of the pancreas?

Answer 26

Exocrine cells- secretion of digestion enzymes Islets of Langerhans- endocrine component of the pancreas

Question 27

What are the three major hormones produced by the Islets of Langerhans?

Answer 27

1. Alpha cells (A cells) secrete the hormone glucagon. 2. Beta cells (B cells) produce insulin and are the most abundant of the islet cells. 3. Delta cells (D cells) secrete the hormone somatostatin in response to peaks of insulin and glucagon. Decreases gut motility

Question 28

What hormones does the pancreas secrete and what is the function of them?

Answer 28

Insulin- increase uptake of glucose into the cell, lowers blood sugar levels Glucagon- promotes glycogenesis and increases blood glucose levels Somatostatin- mild inhibition of insulin and glucagon preventing fluctuations in blood glucose levels

Question 29

What hormone do the ovaries produce and what are its roles?

Answer 29

1. Progesterone – Corpus luteum • Essential for maintenance of pregnancy • Prepares uterus for implantation of fertilised ovum • Acts on mammary tissue to prepare for lactation • Exerts negative feedback – prevents oestrus during pregnancy 2. Oestrogen – walls of the developing ovarian follicles • Causes the behavioural signs of heat • Preparation of genitalia for mating • Negative feedback Relaxin (CL) – preparation for parturition

Question 30

What hormone do the testes produce and what are its roles?

Answer 30

1. Testosterone - Interstitial cells of Leydig responsible for: • Development of male characteristics • Male behaviour • Development of spermatozoa 2. Sertoli cells

Question 31

What hormone do the adrenal glands produce and what are its roles?

Answer 31

``` Adrenal medulla • Adrenaline • Noradrenaline. • Secreted in response to stress • Prepare the body for emergency action • “ fear, fight, flight" response. • Under direction from sympathetic nerves from the hypothalamus. ```

Question 32

What does the adrenal medulla do?

Answer 32

Catecholamines – adrenaline, noradrenaline • Raise blood glucose levels • Break down glycogen stored in the liver – glycogenolysis • Increase the heart rate • The rate and depth of respiration • Increase of the amount of oxygen teaching the tissues • Dilate the blood vessels of the skeletal muscles • Decrease the activity of the GIT and the bladder

Question 33

What are the three steroid groups that are within the adrenal cortex?

Answer 33

• 1. Glucocorticoids – cortisol, corticosterone, cortisone • Present in low levels • Increase in response to stress • Increase blood glucose levels • Stimulate hepatic gluconeogenesis • Mobilising fatty acids from the adipose tissue ready for conversion to glucose • In large quantities they depress the inflammatory reaction • Hyperadrenocorticalism (Cushing’s disease) 2. Mineralocorticoids – aldosterone • Acts on distal convoluted tubule of the kidney • Regulates acid/base balance 3. Adrenal sex hormones (insignificant quantities)

Question 34

What 2 hormones are secreted by the kidneys?

Answer 34

* Calcitriol – increases absorption of Ca and P from digestive tract * Erythropoietin – stimulates bone marrow to produce red blood cells

Question 35

How are hormone levels controlled?

Answer 35

* Too much or too little of the hormones will impair the functioning of the body. * The body uses “Feedback “ loops to control the amount of hormone released * Negative feedback is more usual, positive feedback rarely occurs.

Question 36

How does negative feedback work?

Answer 36

* Rising levels of hormone * Biological response * Inhibition of further hormone release * Straight forward * Regulation of insulin * Complex * Multiple organs in loop * Reproduction

Question 37

How does positive feedback work? Give an example.

Answer 37

``` • Less common • Rising levels of hormone • Biological response • Increase of further hormone release • Not involved in homeostasis eg; giving birth- hypothalamus/ posterior pituitary- oxytocin- cervical delation and uterine contractions- further cervical dilation ```

Question 38

What is hyperfunction?

Answer 38

PRIMARY- caused by hyperplasia, cysts or tumours SECONDARY- caused by tumours in the pituitary gland which controls the relevant effector glands or by imbalances in hormonal control

Question 39

What is hypofunction?

Answer 39

PRIMARY- caused by destruction of secretory glandular cells, development of abnormalities or genetic defects which determine a decrease in hormone synthesis SECONDARY- caused by a destructive lesion in the pituitary gland which in turn determines lesion in the pituitary gland which in turn determines hypo functioning in the respective target gland