Endocrine system II

Question 1

Hormones

Answer 1

• produced by endocrine glands
• secreted directly into the blood
• bind to cell receptors and trigger a response
• indirect communication: ligands bind receptors, cell signalling through signal transduction inside the cell
• same hormones can cause different responses in different cell types

Question 2

Hormone chemical structure (3)

Answer 2

1. Amino acid-based hormones: amino acid derivatives, peptides and proteins
2. steriods: all synthesised from cholestrol, gonadal and adrenocortical hormones
3. Eicosanoids: considered hormones by some scientists, but most classigy it as a paracrine (have effect only in the vicinity of the glands secreting it)

Question 3

Amino-acid derivative hormones

Answer 3

• derivatives of singal amino acids
• catecholamine’s and thyroid hormones
• thyroid hormones: more like steroidal hormones as bind to intracellular receptors
  e. g. epinephrine

Question 4

Peptide and protein hormones

Answer 4

• > 3-200 amino acids
• half-lives short
• H2O soluble, dissolve easily in extracellular easily in extracellular fluid or transport
• lipophobic = so cannot directly enter cell; instead bind to surface receptors
• hormone receptor complex initiates cellular response via signal transduction
  e. g. insulin, parathyroid hormone, anfgiotensin II, atrial-natriretic peptide

Question 5

Steroid hormone

Answer 5

• derived from cholesterol
• lipophilic, so diffuse easily across membranes i.e. parent cell and target cell
• no storage in secretory vesicles but continual synthesis
• steroidal hormones poorly solunle in blood and transported by carrier proteins, e.g. albumins

Question 6

Eicosanoids = hormone-like compounds

Answer 6

• formed form polunsaturated fatty acids with 18, 20 and 22 carbons
• synthesised throughout the body, primary actions autocrine (cell-produced substance that has an effect on the cell by which it secreted) and paracrine (considered “local hormone”)
• other hormones often regulate the synthesis of these compounds
• groups includes prostaglandins, thromboxane and prostacyclin

Question 7

Endocrine glands

Answer 7

• produce hormones
• lack ducts (secretion into blood)
• typically have a rich vascular and lymphatic drainage for rapid dispersal of hormones throughout body
• e.g. pituitary, thyroid, parathyroid, adrenal and pineal glands

Question 8

Pituitary glands

Answer 8

• endocrine gland -> produces hormones
• lack ducts ->secretion directly into blood
• works cloesly with the hypothalamus
• controls the functions of many of the other endocrine glands
• responsible for the production of most hormones
• divided into a posterior and anterior pituitary gland
• middle cranial fossa accommodates the pituitary gland (sphenoid bond)

Question 9

Development of the pituitary gland

Answer 9

1. Outgrowths of tissue begin to appear from the hypothalamus (infundibulum) and the roof of the mouth
2. The 2 outgrowths of tisse start to fuse together
3. the immatrue anterior pituirary lobe separates from the roof of the mouth
4. the anterior and posterior pituitary lobes mature and the bony sella turcica forms

Question 10

Location of the pituitary gland

Answer 10

• hypothalamus located at the base of the brain in the posterior part of the forebrain
• the pituitary is located at the base of the brain within the sella tucica
• the anterior is lobe = anterior pituitary (adenohypophysis)
• the posterior lobe = posterior pituitary (neurohypophysis)

Question 11

the pituitary gland anatomy

Answer 11

• the anterior pituitary is glandular NOT neural tissue
• the anterior lobe is larger than the posterior lobe and has three parts
• pars tuberalis = which forms a sleeve round the pituitary stalk
• pars distalis
• pars intermedia = adjoind the posterior lobe

Question 12

Hypothalamus

Answer 12

• integration centre for many physiological process in the body
• made up of nervous tissue and contains groups of specialised neurons

Question 13

Control of the posterior pituitary

Answer 13

• hypothalamus neural tissue
• preoptic nuclei
• supraoptic nuclei
• paraventricular nuclei
• have axons, which terminate in the posterior lobe of the pituitary
• hormones are synthesised and secreted from the neurones
• the hormones travel from the posterior pituitary via axons in the pituitary stalk
• 2 hormones released = ADH and oxytocin

Question 14

Anterior pituitary communication

Answer 14

• no direct connection between the hypothalamus and the anterior pituitary gland
• communication happens through vasculat connection = network of blood capillaries in the hypothalamus drains into larger portal blood vessels
• some of the neurons in the hypothalamus terminate close to the blood capillaries within the hypothalamus

Question 15

hypothalamic - hypophyseal portal system

Answer 15

• no direct neural connection
• neural of hypothalamus terminating close the blood capillaries within the hypothalamus release hormones into hypothalamic hypophyseal portal system
• hormones like gonadotropin releasing hormone circulate to the anterior pituitary through the hypophyseal portal system
• anterior pituitary receives hypothalamus hormones and the -> regulates secretion of other hormones

Question 16

Anterior pituitary hormones
Corticotrophs
Somatotrophs
Gonadtrophs
Thyrotrophs
Lactotrophs

Answer 16

• anterior pituitary is composed of groups of epithelial cells
• different populations of cells produce different hormones
• corticotrophs = produce ACTh and MSH
• somatotrophs = produce growth hormones (GH)
• gonadtrophs = produce LH and FSH
• thyrotrophs = produce thyroid-stimulating hormone
• lactotrophs = produce prolactin

Question 17

Human Growth Hormone

Answer 17

• growth hormone-releasing hormones
• somatotrophs secrete human growth hormone
• regulates growth in the muscles and bones
• indirectly affects growth
• many body cells (chondrocytes, fat cells, muscle, liver) respond by secreting insulin-like growth factor
• directly affects metabolism
• increases blood glucose levels
• note: GH is released in pulses during the hours of sleep

Question 18

Excess growth hormone

Answer 18

• depending on when excess HGH occurs 2 types:
  1. gigantism: pituitary produces to much growth hormone in early childhood:
• person is> 7 foot, large in all proportions
• so weak that they can harldy stand
  2. acromegaly: pituitary gland produces too much growth hormone during adulthood: causes disfigurement

Question 19

Growth hormone deficiency

Answer 19

• medical condition due to lack of growth hormone
• can be congential or acquired in childhood/adult life
• can be partial or complete
• treatment is by growth hormone replacement = since 1986 recombinant human growth hormone

Question 20

LS and FSH in the female

Answer 20

• Female gonads = ovaries
• GnRh stimulates gonadotropins
• gonadtropins release LH and FSH
• LH stimulates cells in ovaries
• FSH stimulates in the follicles to grow in the ovary
• ovaries release in response ovarian steroir hormones -> orestrogen and progesterone have effects on many other parts of the body (bone, brain, vascular tissue)
• GnRG stimulates release of gonadotropins

Question 21

LH and FSH in the male

Answer 21

• Male gonads = testes
• GnRH stimulates gonadotropins
• Gonadotropins release LH and FSh
• LH stimulate the leydig cells to secrete testosterone
• FSH stimulate the sertoli cells to secrete inhibin

Question 22

TSH

Answer 22

• thyrotropin releasing hormone stimulates the thyrotopin int he anterior pituitary
• thyrotrophs release TSH
• TSH acts on the thyroid gland to stimulate the release of thyroid hormones
• thyroid hormones play an important role in controlling carbohydrate metabolism, fat metabolism and basal metabolic rate including temperature

Question 23

Prolactin

Answer 23

• Prolactin releasing hormone stimulates lactotrophs
• lactotrophs release prolactin
• prolactin intitiates lactation and promotes the growth of the mammary glands, ovaries, testes
• stimulates milk production

Question 24

Adrenocorticotrophic hormone

Answer 24

• controls hormone secretion from the adrenal cortex
• ACTH acts on the adrenal cortex to stimulate the relase of glucocorticoids (mainly cortisol)
• cortisol controls the metabolism of carbohydrates, fats and proteins
• > stress response