Physiology Flashcards
What is autocrine regulation?
Chemicals released from the cells bind to receptors on or in the cell that is releasing them
What is paracrine regulation?
Chemicals released from the cells bind to receptors on adjacent cells
What is endocrine regulation?
Chemicals released from secretory cells are usually transported via the circulatory system
What are hormones?
Any substance produced by one cell to regulate another cell
How does the hypothalamus control endocrine regulation?
Secreted regulator hormones that control the activity of anterior pituitary cells
Synthesises hormones and transports them to the posterior pituitary via the infundibulum
Direct neural control function - controls secretion of adrenaline and noradrenaline by the adrenal medulla
What is diurnal control?
Where external cues (light/dark) evoke fluctuations in hormone secretions
What is an examples of hormones having complementary actions?
Adrenaline, cortisol and glucagon have complementary actions on blood glucose levels
What is an examples of hormones having antagonistic actions?
Insulin and glucagon have antagonistic effects on blood glucose levels
What are the 3 classes of hormones?
Steroids
Amine derived
Proteins
What are steroid hormones?
Lipids derived from cholesterol
How are steroid hormones transported?
In blood plasma by binding to carrier proteins
Some (10%) are free and biologically active
What are examples of steroid hormones?
Cortisol
Oestrogen
Testosterone
How do steroid hormones pass through plasma membranes?
Activated hormone-receptor complex forms within the cell
The complex binds to DNA and activates specific genes - gene activation leads to production of key proteins
What are amine derived hormones?
Hydrophilic hormones derived from amino acids
How are amine derived hormones transported?
Unbound in blood plasma
Where are amine derived hormones secreted from?
Thyroid and adrenal medulla
What are examples of amine derived hormones?
Thyroxine
Adrenaline
What are peptide hormones?
Hydrophilic hormones that make up the majority of hormones
The same thing as protein hormones
Where are peptide hormones secreted from?
Pituitary gland, parathyroid gland, heart, stomach, liver, kidneys
In what form are peptide hormones secreted as?
Precursor molecules and stored in secretory vesicles
What are examples of peptide hormones?
Somatostatin
Insulin
What is the process of insulin secretion?
- Elevation of blood glucose concentration
- Increased diffusion of glucose into the b-cell (aka B-cell) by facilitated transport (GLUT2)
- Phosphorylation of glucose by glucokinase
- Glycolysis of glucose-6-phosphate in mitochondria yielding ATP
- Increased ATP/ADP ratio within cell closes ATP-sensitive K+ channels causing membrane depolarisation
- Opening of voltage-activated Ca2+ channels increases intracellular Ca2+ that triggers insulin secretion
What is the purpose of the binding of hormones to career proteins?
Facilitation of hormone transport
Increased half-life
A reservoir for the hormone
What are examples of specific carrier proteins?
Cortisol-binding globulin binds cortisol selectively
Thyroxine-binding globulin binds thyroxine (T4) selectively
Sex steroid-binding globulin binds mainly testosterone and oestradiol
What are the hormones secreted by the hypothalamus?
Thyrotropin releasing hormone (TRH)
Corticotropin releasing hormone (CRH)
What are the hormones released by the pituitary gland?
Thyroid stimulating hormone (TSH) Adrenocorticotrophic Hormone (ACTH) Luteinizing Hormone (LH) Follicle Stimulating Hormone (FSH) Growth Hormone (GH) Prolactin Melanocyte Stimulating Hormone (MSH) Oxytocin Antidiuretic Hormone (ADH)
What are the hormones released by the pineal gland?
Melatonin
What are the hormones released by the thyroid/parathyroid glands?
Thyroxine (T4)
Triiodothyronine (T3)
Calcitonin (CT)
Parathyroid Hormone (PTH)
What are the hormones released by the adrenal medulla?
Adrenaline (epinephrine)
Noradrenaline (norepinephrine)
What are the hormones released by the adrenal cortex?
Dehydroepiandrosterone (DHEA)
Aldosterone
Glucocorticoids (cortisol, corticosterone
What are the hormones released by the testes?
Testosterone
What are the hormones released by the pancreas?
Insulin
Glucagon
Somatostatin
What are the hormones released by the ovaries?
Oestradiol
Oestriol
Progesterone
Testosterone
What are the hormones released by the placenta?
Human Chorionic Gonadotrophin (hCG)
Oestradiol
What are the hormones released by the mammary glands?
Oestrogen
What is the cause of Diabetes mellitus (Type I)?
Lack of insulin
What is the cause of Diabetes mellitus (Type II)?
Insulin resistance, overproduction of glucose or abnormal insulin secretion
What is the cause of Diabetes insipidus (pituitary)?
Lack of ADH
What is the cause of Diabetes insipidus (nephrogenic)?
Renal unresponsiveness to ADH
What is the cause of Addison’s disease?
Adrenal destruction/lack of ACTH secretion
What is the cause of Cushing’s syndrome?
Adrenal tumour (excess cortisol secretion)
What is the cause of Congenital hypothyroidism?
Lack of T4-T3 secretion
What is the cause of Myxedema (adult hypothyroidism)?
Lack of T4-T3 secretion
What is the cause of Hyperthyroidism?
Excess of T4-T3 secretion
What is the cause of Hypoparathyroidism?
Parathyroid gland destruction
What is the cause of hyperparathyroidism?
Parathyroid gland tumour, increased PTH secretion
What is the cause of Conn’s disease (hyperalosteronism)?
Adrenocortical tumour, excess aldosterone secretion
Which hormone acts on the adrenal gland, which hormone triggers its release, and which hormone does it stimulate the production of?
ACTH
CRH
Cortisol
Which hormone acts on the thyroid gland, which hormone triggers its release, and which hormone does it stimulate the production of?
TSH
TRH
T3/4
Which hormones act on the ovaries and testes, which hormone triggers their release, and which hormones do they stimulate the production of?
LH, FSH
GnRH
Oestradiol, Testosterone
Which hormone is responsible for growth and which hormone triggers its release?
GH
IGF-1
Which hormone acts on the mammary glands and which hormone triggers its release?
Prolactin
Dopamine INHIBITS release of prolactin
What hormones are measured in a normal pituitary blood test?
TSH fT4 LH FSH Testosterone GH IGF-1 PRL
What are the key reproductive hormones?
GnRH LH FSH Oestrogen Progesterone Testosterone
What are the gonadotrophin hormones?
LH, FSH
What are the functions of FSH in males and females?
Males: stimulates testes to produce sperm (spermatogenesis)
Females: causes growth of ovarian follicles (oogenesis) and stimulates the ovary to secrete oestrogen
What are the functions of LH in males and females?
Males: causes the testes to secrete testosterone
Females: causes ovulation and causes progesterone production by the corpus luteum
What is the female HPG (hypothalamic-pituitary-gonadal) axis?
Hypothalamus released GnRH, which stimulates the pituitary to release LH and FSH.
LH and FSH stimulate the ovaries to secrete oestrogen and progesterone.
High levels of oestrogen and progesterone both inhibit and stimulate the pituitary and hypothalamus at different parts in the cycle
What is the male HPG (hypothalamic-pituitary-gonadal) axis?
Hypothalamus released GnRH, which stimulates the pituitary to release LH and FSH.
LH and FSH stimulate the testes to produce testosterone.
High levels of testosterone inhibit the hypothalamus and pituitary
What is GnRH?
Gonadotrophin Releasing Hormone is a neuropeptide synthesised and released by the hypothalamus
In what way is GnRH release different in males and females?
In males: secretes in pulses at a constant frequency
In females: secreted in pulses which vary in frequency during the menstrual cycle
How is frequency of GnRH pulses regulated?
Growth of follicles increases oestrogen concentration, which will increase GnRH pulsatality, driving release of LH
The corpus luteum causes increase in progesterone concentration, which reduces frequency of GnRH pulses
How do the levels of different hormones change throughout the menstrual cycle?
At the start FSH rises, causing growth of ovarian follicles which secrete oestrogen, increasing levels
Rising oestrogen levels cause negative feedback loop to lower FSH temporarily
Once oestrogen reaches a certain level it causes a positive feedback mechanism to increase FSH levels and cause a surge in LH
LH surge causes ovulation and the formation of corpus luteum, which secretes progesterone
Increased levels of progesterone decrease LH secretion
If fertilisation doesn’t occur progesterone levels drop again
What is a follicle?
Oocyte surrounded by follicular cells
What is the function of the negative then positive feedback of FSH levels?q
To select one follicle to be secreted
What happens to the corpus luteum is pregnancy does not occur?
Becomes the corpus albicans
What are the functions of oestrogen?
Increase the thickness of the vaginal wall
Regulate the LH surge
Reduce vaginal pH through increased lactic acid production
Decrease viscosity of cervical mucus to facilitate sperm penetration
What are the functions of progesterone?
Maintains thickness of the endometrium
Responsible for infertile thick mucus to prevent sperm transport and help prevent infection
Relaxes the myometrium (smooth muscle)
What factors regulate sperm’s ability to penetrate the mucus?
Thickness of the mucus
Motility of sperm
Interaction with reactive oxygen species produced by leukocytes int he cervical mucus
Interaction with mucins
Where does spermatogenesis occur?
Seminiferous tubules in the testes
Roughly how long does spermatogenesis take?
70 days
What is the function of testosterone in spermatogenesis?
Stimulates release of spermatocytes from sertoli cells
Maintains the integrity of the blood-testis barrier
How is testosterone produced?
LH stimulates testosterone production from cholesterol in Leydig cells
How are testosterone and LH linked?
Negative feedback - rise in testosterone decreases LH and decrease in testosterone increases LH
