Hormones, homeostasis, and reproduction

- Homeostasis is the physiological variables that stay within a certain limit

- IE: blood pH, blood carbon dioxide concentration, blood glucose concentration, body temperature (37), water balance within tissue

- Negative feedback: the physiological process that brings a value back towards to a set point 

- Nervous system and Endocrine system work to keep homeostasis

- Hormones are transported by the bloodstream from the gland, where it is produced, to the specific target cell 

- gland is located in your neck

- Thyroxin created from an amino acid and iodine; signals from the hypothalamus

- used for basal metabolic rate; achieve by stimulating carbohydrate and lipid metabolism via the oxidation of glucose and fatty acid; helps to regulate body temp 

- Thyroxin exists in two forms: T3 and T4 which indicate the number of iodine atoms within the structure; insufficient iodine in diet is bad

- T4 is typically converted to T3 in the target cell

- T3 enters the nucleus of cell and acts as a transcription regulator; leads to increase in messenger (m)RNA; increase in proteins; increase in the metabolism of the cell

- cells under the influence need greater volume of oxygen

- Hyperthyroidism and Hypothyroidism and goitre 

- Leptin produced by adipose (fat) tissues

- more fat stored; more leptin produced and secreted into the bloodstream

- target cells in hypothalamus of brainstem; binds to receptors on the hypothalamus

- leptin lowers appetite and reduces food intake

- obese people should have an increased leptin circulating but cells have been desensitized so don't recognize leptin

- double blind study

- Pineal gland regulates their daily 24 hour cycle activity (Circadian rhythm)

- Melatonin is secreted from here

- little melatonin in daytime; high melatonin at night

- highest production is 2am and 4am

- exposure to light can change circadian rhythm

- Person who is jet lag can take melatonin pills to alter circadian rhythm

- both hormones produced and secreted by pancreas

- these regulate blood glucose levels

- when you eat glucose is absorbed into the blood stream in the capillary beds of the villi of the small intestine increasing blood glucose level

- works by negative feedback

- in the intestinal villi, glucose travels to hepatic portal vein which takes the blood to the liver

- hepatic portal vein is the only blood vessel that has large fluctuations in bgl

- hepatocytes (in the liver) processes the glucose and are triggered by insulin and glucagon

- beta cells in the pancreas sense an increase/decrease in glucose

If BGL goes above:

- Insulin opens protein channels in cell plasma membrane; allows glucose to diffuse into cell by facilitated diffusion

- Insulin also stimulates the hepatocytes to take in glucose and convert it to glycogen; glycogen stored as granules int he cytoplasm of the hepatocyte; same thing happens in the  muscles

If BGL goes below:

- glycogen made and stored by liver is needed in the body

- alpha cells of pancreas begin to produce and secrete the hormone glucagon 

- glucagon stimulates hydrolysis of the granules of glycogen stored in hepatocytes and muscle cells; hydrolysis produces the monosaccharide glucose

- glucose enters blood

- characterized by hyperglycemia (high blood glucose)

- Cause: Type1 due to immune system destroying beta cells of the pancreas and do not produce sufficient insulin; Type2 caused by body cell receptors that do not respond to insulin

- people with untreated diabetes have sufficient glucose in their body but not in the body cells

- Treatment: Type1 controlled by injections; Type2 due to controlled diet

- untreated: damage to the retina, blindness, kidney failure, nerve damage, risk of cardiovascular disease, poor wound healing

- used leptin as experimental hormone

- hypothesis: Obese individuals have high levels of circulating leptin and are resistant to the weight-reducing effect of leptin 

- organism: randomized, double-blind, placebo-controlled cross-over study of 27 women who were at least 18 months post RYGB and lost on average 30% of their presurgical body weight 

- Conclusion: there was to significant effect of leptin treatment on body weight in women with relative hypoleptinemia after RYGB 

- Pituitary hormones (FSH and LH) released from anterior pituitary gland; acts on the ovaries to develop follicles

- Ovarian hormones (oestrogen and progesterone) released from the ovaries; act on the uterus to prepare of pregnancy

FSH: stimulates follicular growth in ovaries, stimulates oestrogen secretion from develping follicles

LH: surge causes ovulation, results in the formation of corpus luteum

Oestrogen: thinkens uterine lining (endometrium), inhibits FSH and LH for most of cycle, stimulates FSH and LH release pre-ovulation

Progesterone: thinkens uterine lining (endometrium), Inhibits FSH and LH

1. Follicular Phase: 

- FSH secreted from AP; growth of ovarian follicles

- dominant follicle produces oestrogen inhibiting FSH secretion (negative feedback)

- oestrogen acts on the uterus to stimulate thickening of endometrial

2. Ovulation

- day 12: oestrogen stimulates AP to secrete hormones (positive feedback)

- large surge of LH and less FSH

-LH cause dominate follicles to rupture and release egg

3. Luteal Phase

- ruptured follicle develops into a slowly degenerating corpus luteum

- this secretes high levels of progesterone and lowers levels of oestrogen

- oestrogen and progesterone act on uterus to thicken endometrial lining (preparing for preg); these two inhibit secretion of FSH and LH preventing follicles from developing

4. Menstruation

- if fertilisation occurs, the developing embryo will implant in endometrium and release hormones to sustain corpus luteum

- if fertilisation doesnt occur, the corpus luteum degenerates; oestrogen and progesteron levels drop; endometrial layer shed into menstrual blood; oestrogen and progesterone levels low to inhibit the anerior pituitary and cycle begins again

- GH (aka somatotropin) a protein that stimulates cells to enlarge and divide faster

- enhanced the movement of amino acids through cell membranes and increase rate of protein synthesis

- decreases the rate at which cells use carbohydrates and increase the rate at which they use fats

- peaked secretion at night

- hypothalamus secretes GHRH stimulates GH secreting

- ** inhibits secretion

- it is a protein and promotes milk production

- high levels of it can disrupt sexual functions

- Prolactin secretion is mostly under inhibitory control by dopamine from the hypothalamus (aka prolactin release inhibiting hormone)

- hypothalamus likely releases more than one prolactin-releasing factor (PRF)

- causes or strengthen labour contractions during childbirth

- positive feedback example

- controls bleeding after childbirth

- can be used to induce abortion

- also helps with lactation

- stimulated in the SNS and it sends a signal to the Adrenal Medulla which releases epinephrine or norepinephrine this causes flight or flight response

- flight or flight include: dilated airways, increase heart-rate, pupil dilation, Lungs RR

- small peptide molecule made in hypothalamus released by pituitary gland 

- prevents production of dilute urine; it causes more permeable membrane to soak up more water

- can stimulate contraction of arteries and capillaries

- known as vasopressin

Steroid Hormones

- can freely diffuse across the plasma membrane of cell

- bind to receptor in cytoplasm or nucleus of target cell to make active receptor-hormone complex which move into the nucleus and bind directly to DNA, acts as a transcription for gene expression

Peptide Hormones

-  hydrophylic and lipophobic meaning they cant freely cross the plasma membrane

- bind to receptors on surface of cell which typically have internally anchored proteins

- receptor complex activates a series of intracellular molecules which initiate cell activiy 

- process called signal transduction 

- IE: insulin, glucagon, leptin, ADH, oxytocin

Amine Hormones

- derived from the amino acid tyrosine and include adrenaline, thyroxin and triiodothyronine

- Amine hormones do not share identical properties and have properties common to both peptide and steriod hormones

AP releases these:

- Adrenocorticotropic hormone (ACTH) aka: corticotropin

- Follicle-stimulating hormone (FSH) aka: Follitropin

- Growth hormone (GH) aka: somatotropin (STH)

- Luteinizing hormone (LH) aka: Lutropin

- Prolactin (PRL)

Secretes these:

- Antidiuretic hormone (ADH) aka: vasopressin

- Oxytocin (OT)