The Endocrine Sytem Flashcards
What did Prof. Brown-Sequard do in 1889?
Self-administered 5 injections of dog testicle extract and 5 injections of guinea-pig testicle extract. He claimed that this increased his physical strength, improved his intellectual capacity, and increased his sexual potency
Define Glands
Epithelial tissue derivatives specialised for secreting
Define Secretion
Biochemical release from a particular type of cell upon stimulation
Define Endocrine and give an example
Endo = internal, crine = secretion. Secretions enter the bloodstream from a ductless gland. For example, pancreas releases insulin into the blood
Define exocrine and give an example
Gland with ducts that channel its secretion (exocrine glands have ducts and secrete secretion into local area). For example, salivary gland
Define hormones
Chemical messengers that are secreted into the blood by endocrine glands in response to an appropriate signal, and exerting their effects on target cells that have receptors that bind with the hormone
What are the two classifications of hormones?
Solubility and structure
How are hormones classified based on solubility? Give examples
- Hydrophilic or water soluble. For example, peptides (eg insulin) and catecholamines (adrenaline and noradrenaline)
- Lipophilic or lipid soluble. For example, steroids (eg cortisol) and thyroid hormone
How are hormones classified based on their structure? Give examples
- Peptides - chain of specific amino acids
- Amines - derivatives of amino acids, tryptophan or tyrosine (indoleamines, catecholamines, thyroid hormones)
- Steroids - cholesterol derived lipids
Compare how peptide and steroid hormones are produced
Peptide - produced by normal protein synthesis machinery (central dogma)
Steroid - produced by modification of cholesterol molecule by enzymes
Compare how peptide and steroid hormones travel
Peptide - travel in blood in solution
Steroid - travel in blood bound to plasma proteins
Compare how peptide and steroid hormones enter cells
Peptide - cannot enter cells (lipid bilayer cell membrane)
Steroid - enter cells easily
Compare how peptide and steroid hormones interact with receptors
Peptide - bind to cell surface receptor
Steroid - Intracellular receptor
Compare how peptide and steroid hormones cause action
Peptide - trigger event on inside surface of membrane (second messenger system)
Steroid - Act on DNA to alter cell function
Compare the speed of peptide and steroid hormones
Peptide - fast acting
Steroid - slow acting (transcription delay)
Why can contraception and thyroid hormones be taken as pills?
Contraceptive pills and patches contain oestrogen and progesterone which are steroids and can be absorbed through the skin and get into systemic circulation without being broken down in the GI tract.
Thyroid hormones are amines and are not broken down by enzymes in the GI tract and hence can be taken as pills
Why is insulin taken as in injection?
Because insulin is a peptide hormone so should be administered through intravenous, subcutaneous or intramuscular routes
List the regulatory roles of the endocrine system
- Metabolism, water and electrolyte balance
- Stress response
- Growth and development
- Reproduction
- Red cell production
- Coordination of circulation
- Coordination of digestion
What size is the hypothalamus and pituitary?
Pea size (1cm^2)
How much does the hypothalamus and pituitary weigh?
1g
What are the two lobes of the pituitary?
Anterior and Posterior
What are the connections of the anterior and posterior pituitary?
Anterior = vascular connection
Posterior = neural connection
How is the pituitary connected to the hypothalamus?
Via the pituitary stalk
What is the HPG Axis?
Hypothalamus-Pituitary-Gonad Axis
Hypothalamus -> Anterior Pituitary ->FSH and LH -> Ovary (->oestrogen) Testes (->testosterone)
What is the HPT Axis?
Hypothalamus-pituitary-thyroid axis
Hypothalamus -> Anterior pituitary -> TSH -> Thyroid Gland -> Thyroid hormones
What is the HPA Axis?
Hypothalamus-pituitary-adrenal axis
Hypothalamus -> Anterior pituitary -> ACTH -> Adrenal gland -> Adrenocorticosteroids
What are the functions of the hypothalamus?
Control of pituitary hormone release. Interface between events inside and outside the body and their endocrine response
What hormones are involved with the hypothalamus?
Corticotrophin releasing hormone (CRH)
Thyrotropin releasing hormone (TRH)
Somatostatin
Gonadotrophin releasing hormone (GnRH)
Growth hormone releasing hormone (GNRH)
Prolactin releasing hormone (PRH)
Prolactin inhibiting factor (dopamine)
What are the functions of the anterior pituitary?
Controls activity of other endocrine glands
Ovulation and pregnancy (females)
Sperm production (males)
Growth
What hormones are involved with the anterior pituitary?
Thyrotropin or thyroid stimulating hormone (TSH)
Adrenocorticotrophic hormones (ACTH)
Luteinising hormone (LH)
Follicle stimulating hormone (FSH)
Growth hormone (GH)
Prolactin
What are the functions of the posterior pituitary?
Involved in regulating overall water balance
Uterine concentration
Ejection of milk
What hormones are involved with the posterior pituitary?
Antidiuretic hormone (ADH) or vasopressin oxytocin
Define gonads
Male and female reproductive organs that secrete hormones and are sites of sperm and ova production
What hormone is released by the testis?
Testosterone
What are the functions of the testis?
Masculinizes the reproductive tract and external genitalia during the foetal period
Promotes growth and maturation of the reproductive system at puberty
Spermatogenesis
Develops sex drive
Secondary sexual characteristics
Protein anabolic effect and bone growth during puberty
What hormones are released by the ovaries?
Oestrogen and progesterone
What are the functions of the ovaries?
Maturation and maintenance of reproductive system
Female secondary sexual characteristics
Ova maturation and release
Transport of sperm to the site of fertilization
Preparing the uterus for the development of embryo and foetus
Contributing to the breasts ability to produce milk
What hormones are involved in the HPG Axis when regulating testicular function?
GnRH (Gonadotropin-releasing hormone)
FSH (Follicle-stimulating hormone)
LH (Luteinizing hormone)
What regulates FSH and LH?
Testosterone level in the blood regulate both FSH and LH
Inhibin only regulates FSH
Draw out and explain the HPG axis when regulating testicular function
See notes
Where is the thyroid gland located?
In the neck area, over the trachea, and just below the larynx
What is the thyroid gland made up of?
Two lobes of endocrine tissue joined by an isthmus (narrow part of the gland)
How are hormone-secreting cells arranged in the thyroid gland?
In hollow spheres called follicles
What are the two thyroid hormones?
Thyroxine (T4) and triiodothyronine (T3)
What are the main components of the thyroid hormones?
Amino acid tyrosine and iodine (comes from diet)
What are the functions of the thyroid hormones?
Increasing metabolic rate and heat production (calorigenic effect)
Sympathomimetic effect (permissive action)
Effect on cardiovascular system
Effect on growth and nervous system
Draw out and explain how thyroid hormones are regulated
See notes
What are the effects of the parathyroid hormone (PTH)?
Calcium metabolism
Raises free plasma Ca2+
Mobilises bone store
Reduces urine loss
Increases gut absorption
Where are the adrenal glands (Suprarenal glands) located)
There are two adrenal glands and they are located one above each kidney, embedded in a capsule of fat
Why are the kidneys an endocrine gland?
Because they secrete hormones
What are the two regions of the adrenal gland?
Adrenal cortex and adrenal medulla
What hormones are secreted by the adrenal cortex?
Steroid hormones:
Mineralocorticoids (aldosterone)
Glucocorticoids (cortisol)
Sex hormones (DHEA)
What are the functions of the adrenal cortex?
Aldosterone: Blood pressure regulation through Na+ retention and K+ elimination by kidneys
Cortisol: Metabolic effects in increasing blood glucose level, breakdown of proteins and lipids. Permissive action for catecholamine function. Role in adaptation to stress. Anti-inflammatory and immunosuppressive effects
DHEA: Androgen-dependent process in females
What hormones are secreted by the adrenal medulla?
Catecholamines (adrenaline and noradrenaline)
What are the functions of the adrenal medulla?
Adrenaline and Noradrenaline: Reinforce the sympathetic nervous system (fight or flight response). Stress response. Regulation of blood pressure. Fuel metabolism
Draw out and explain the HPA Axis
See notes
Draw out and explain the integrated stress response
See notes
What is the menstrual cycle?
A recurring cycle of events in uterus and ovaries under the influence of hormones in females (Menstruus means “monthly”)
What are ovarian follicles made of?
Many sac-like structures called ovarian follicles
What do ovarain follicles contain?
Oocyte and cells that produce oestrogen and progesterone
What cells produce oestrogen and progesterone? And what stimulates these cells to do the above?
Thecal cells and granulosa cells produce oestrogen and progesterone when stimulated with FSH and LH
What are the stages of ovarian follicle development?
Primordial follicle -> Primary follicle -> Secondary follicle -> Graafian follicle (mature follicle) -> Ovulation
How long does it take for a primordial follicle to become a primary follicle?
13-50 years
How long does it take for a primary follicle to become a secondary follicle?
45 days
Draw a diagram showing the stages of oogenesis
See notes
Draw and explain a diagram showing the effects of the HPG axis on the early follicular phase (pre-ovulation)
See notes
Draw and explain a diagram showing the effects of the HPG axis on the late follicular phase (just before ovulation)
See notes
Describe what happens when there is an LH surge?
- Re-starts meiosis in the oocyte… which becomes haploid
- Activates enzymes - dissolve follicle wall and promote vascular leakage so that the antrum swells and bulges
- Follicle ruptures
- Ovulation
- Oestrogen production dives
What are the effects of progesterone?
- Inhibits FSH and LH, stopping further follicle development and ovulation in current cycle
- Prepares uterus for pregnancy (should fertilization occur)
What is the function of the corpus luteum?
Source of oestrogen and progesterone in luteal phase
What are the effects of low doses of oestrogen in the combined contraceptive pill?
- Decreased FSH from anterior pituitary
- Decreased development of follicle
- No ovulation
What are the effects of progestogens in the combined contraceptive pill?
- Makes cervical mucus sperm-unfriendly
- Decreased LH from anterior pituitary
- Decreased GnRH from hypothalamus
- Decreased motility of fallopian tube
What is in the progestogen-only pill?
Low dose of progestogen taken continuously (eg either norethisterone or levonorgestrel)
What are the effects of the progestogen-only pill?
- Makes cervical mucus unhospitable to sperm;
- Hinders implantation; through its effect on the endometrium and on the motility and secretions of the fallopian tubes;
- Menstruation often ceases initially but usually returns with prolonged use;
- Main adverse effects: Breakthrough bleeding and irregular menses
What happens during the proliferative phase?
Oestrogen:
- Promotes growth of endometrium and myometrium
- Promotes formation of progesterone receptors
What happens during the secretory, or progestational, phase?
Progesterone acts on the oestrogen-primed endometrium:
- Loosens and softens connective tissue - makes implantation easier
- Promotes secretion of nutrients (glycogen)
- Quietens uterine activity
What happens during the menstrual phase?
- No occupants… (no embryo) no hCG so Corpus Luteum degenerates
- Progesterone (and oestrogen) support lost
- Uterine prostaglandins -> vasoconstriction -> tissue death
- Blood and endometrial debris (menses) lost through vagina
What is Dysmenorrhea?
Painful periods
What is Menorrhagia?
Heavy or prolonged periods
What is Amenorrhea?
Absence of periods (primary or secondary)
What is Oligomenorrhea?
Light periods
