6.6 Hormones, homeostasis and reproduction Flashcards
The Endocrine System
A stimulus is received and processed.
Hormones are secreted directly into the blood.
They are carried to the target tissues.
The action of the hormone changes the condition of the tissue.
This change in monitored through feedback.
Most hormonal change results in negative feedback (corrects the imbalance)
Key endocrine glands:
Pineal gland
Pituitary gland
Thyroid gland
Thymus
Adrenal gland
Pancreas
Ovary (female)
Testes (male)
Blood glucose is maintained through the actions of the…
pancreas and the liver
Pancreatic hormones insulin and glucagon regulate …
blood glucose levels
islets of Langerhans
small regions of the pancreas that secrete hormones directly into the blood
If blood glucose levels DROP:
pancreas detects drop
𝛂 cells create/secrete glucagon hormone
glucagon stimulates the liver to convert stored glycogen into glucose and its release into the blood
blood glucose increases (to normal)
If blood glucose levels RISE:
pancreas detects rise
β cells create/secrete insulin
Insulin stimulates uptake of glucose by various tissues (skeletal/muscle)
Insulin stimulates liver to convert blood glucose into stored glycogen
blood glucose drops (to normal)
Diabetes
consistently elevated blood glucose levels
Damages tissues and their proteins
Prevents water reabsorption in kidneys 🡪 increase in volume of urine & body dehydration
Symptoms: constant urination, constant thirst, tired, craves sugar, glucose in urine
Type I diabetes (early onset)
Cannot produce enough insulin
Autoimmune disease
Destruction of β cells in islets of Langerhans by immune system
Treatment
Testing blood glucose levels regularly and injecting insulin when too high
Implant devices to release insulin
Stem cell treatment to create new β cells
Type II diabetes (late onset)
Cannot respond to insulin
Lack of insulin receptors or glucose transporters on target cells
Risk factors: sugary/fatty diets, prolonged obesity, genetic factors that affect metabolism
Treatment
Adjusting diet
Frequent, smaller meals
Avoid sugary foods
Eat foods with low glycemic index (digested slowly
High fiber foods
Exercise
Type II diabetes (late onset)
Cannot respond to insulin
Lack of insulin receptors or glucose transporters on target cells
Risk factors: sugary/fatty diets, prolonged obesity, genetic factors that affect metabolism
Treatment
Adjusting diet
Frequent, smaller meals
Avoid sugary foods
Eat foods with low glycemic index (digested slowly
High fiber foods
Exercise
Thyroxin
Produced by: thyroid gland
Structure: four iodine atoms
Targets: most body cells (liver, muscle, brain)
Effects:
increases metabolic rate/rate of protein synthesis
increases heat production when body temp. is low (e.g. increased respiration)
Thyroxin deficiency (hypothyroidism)
Tired/lack of energy
Forgetfulness
Depression
Decrease appetite & weight gain (less glucose/fat broken down by cell respiration)
Feel cold
Constipation (muscle contractions in gut slow down)
Impaired brain development in children
Leptin
Produced by: adipose cells (fat storage cells)
Targets: appetite control centre of the hypothalamus (in brain). Leptin binds to receptors in cell membranes
Effects:
Increase in adipose tissue increases leptin secretions into the blood
Appetite inhibition → reduced food intake
Mice and leptin
Mice with two recessive alleles ob/ob were found to be obese
Wild-type allele supports synthesis of leptin
ob/ob mice injected with leptin showed decline in appetite
Melatonin
Produced by: pineal gland in darkness
Controlled by: suprachiasmatic nuclei (SCN) in the hypothalamus
Targets: pituitary and other glands
Effects:
synchronization of circadian rhythms (24-hr cycle)
Circadian rhythms
Controlled by two groups of cells in the hypothalamus (brain)
Control secretion of melatonin by pineal gland to regulate sleep cycle → increases at night, decreases at dawn
increase in melatonin at night drops body temp. and possibly reduces urine production
Light detected by retina helps to set circadian rhythm
Even if kept in environment without light cues, body’s circadian rhythm will be mostly maintained
Sex determination
in embryos the first appearance of the gonads is essentially the same in the two sexes. Gonads could become either ovaries or testes.
SRY gene
encodes for a protein known as testis determining factor (TDF).
TDF
is a DNA binding protein which acts as a transcription factor promoting the expression of other genes that cause testis development..
In the absence of TDF
the gonads become ovaries and the developing fetus becomes female.
Testosterone
The testes develop from the embryonic gonads when the the embryo is becoming a fetus. They develop testosterone-secreting cells.
The testes secrete testosterone which causes the male genitalia to develop.
At puberty the secretion of testosterone increases causing:
The primary sexual characteristic of sperm production in the testes
Development of secondary sexual characteristics such as enlargement of the penis, growth of pubic hair and deepening of the voice
Estrogen and progesterone
n the absence of fetal testosterone and the presence of maternal estrogen and progesterone, female reproductive organs develop (ovaries develop from the embryonic gonads) due to:
estrogen and progesterone
No testosterone
Estrogen and progesterone are present. At first they are secreted by the first by the mother’s ovaries and later by her placenta.
At puberty the secretion of estrogen and progesterone increases causing:
Primary sexual characteristic of egg release
Development of female secondary sexual characteristics such as enlargement of the breasts and growth of pubic hair
uterus
provides protection, nutrients and waste removal for the developing fetus
Muscular walls contract to aid birthing process
oviduct (fallopian tube)
Connects the ovary to the uterus
Fertilisation of the egg occurs here
ovary
Produce eggs, estrogen and progesterone
endometrium (lining of the uterus)
develops each month in readiness for the implantation of a fertilised egg
