THE ENDOCRINE SYSTEM HTTP://WWW.YOUTUBE.COM/WATCH?V=WVRLHH14Q3O
Chapter 10
THE ENDOCRINE SYSTEM
Contributes to: control of growth,
development, reproduction, behaviour, energy metabolism, and water balance
By: Secreting hormones
To control Organ and tissue
functions
ENDOCRINE SYSTEM A system of ductless
secretory organs (glands) located in various parts of the body
Include Pineal, anterior/posterior
pituitary, thyroid, parathyroid, thymus, adrenal, islets of Langerhans, ovaries, testes, mammary
Main function Secrete hormones directly into
the blood or extracellular fluid
HYPOTHALAMUS Is not a gland but a region of the brain Part of the nervous system Very important for function of endocrine system Produce neurohormones that stimulate or inhibit
production of other hormones in the pituitary gland
HORMONES OF THE HYPOTHALAMUS
Thyrotropin-releasing hormone (TRH) Stimulates release of thyroid-stimulating hormone (TSH)
Gonadotropin-releasing hormone (GnRH) Stimulates release of follicle-stimulating hormone (FSH)
and luteinizing hormone (LH) Growth hormone-releasing hormone (GHRH)
Stimulates release of growth hormone (GH) Corticotropin-releasing hormone (CRH)
Release of adrenocorticotropic hormone (ACTH) Somatosin
Inhibits the release of growth hormone (GH) Dopamine
Inhibits the release of thyroid-stimulating hormone (TSH)
HORMONES: MAINTAINING HOMEOSTASIS
Chemical management system for the body Chemicals produced by cells in one part of the body
the regulate the processes of cells in another part of the body
Chemical messengers – act on cells from another part of the body
Local regulators – act on nearby cells Self regulators – cells that produce chemicals
to stimulate their own cellular processes
HORMONES Produced and secreted by
cells, tissues and organs that compose the endocrine system (glands) directly into the blood or extracellular fluid
Hormones are circulated throughout the body
Only target cells will respond to specific hormones
Hormones are broken down by enzymes in target cell, liver or kidneys where they are reused or excreted
HORMONES
Secreted in an inactive form – prohormones
Prohormones are converted by target cells or by enzymes in the blood to an active form
Angiotensinogen → angiotensin
HORMONES Protein hormones
Consist of AA – 3 to 200 in length
Usually hydrophilic – water soluble
Diffuse well through blood Steroid hormones
Derived from cholesterol Not water soluble Usually encased with protein
to travel through blood Pass easily through lipid
bilayer
HORMONE MECHANISMS Water-Soluble
Cannot pass membrane Bind to receptor molecules in the
cell membrane Signal is activated Secondary messenger is
activated Change is caused inside cell Acts in the cytosol or the nucleus
Glucagon Breakdown of glycogen into
glucose
HORMONE MECHANISMS Lipid-Soluble
Can pass membrane (lipid) Bind to receptors inside a cell
(cytosol or nucleus) Turn on or off an action of a
specific gene Changes amount of protein
that is synthesized by cell Aldosterone
Increase sodium absorption → increases water retention → increase blood pressure
MAJOR FEATURES OF HORMONE MECHANISMS
Only the cells that contain surface or internal receptors for the hormones respond to the hormones
Once bound to their receptors, hormones produce a response by turning cellular processes on or off. They do this by altering the proteins that are functioning in or produced by the cell
Hormones are effective in very small concentrations because of the amplification that occurs in both the surface and internal receptor mechanisms
The response to a hormone differs among target organs and among species
HORMONES: NEGATIVE FEEDBACK MECHANISMS
Secretion of hormones are regulated by negative feedback mechanisms
Hormones inhibit other hormones Multiple hormones can be secreted at a
time
THE PITUITARY GLAND
The Master Gland Produces hormones that control most of
the other endocrine glands
THE PITUITARY GLAND
Made up of anterior lobe and posterior lobe
Links endocrine system to nervous system via portal vein (hypothalamus)
Influenced by hypothalamus Releasing
hormones/inhibiting hormones
2. portal vein4. anterior
pituitary gland5. hypophyseal
vein6. posterior
pituitary gland8. pituitary stalk9. capillary
network10. neurons11. neurosecretory
cells12. hypothalamus
ANTERIOR PITUITARY GLAND Secretes 6 major
hormones into the bloodstream which influence hormone secretion in other glands Prolactin, growth hormone,
thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone
Other hormones produced Melanocyte-stimulating
hormone, endorphins
GROWTH HORMONE Cell division, protein
synthesis, bone growth IGF – insulin growth
factor that stimulates these functions
Also Conversion of glycogen to
glucose, fats to fatty acids – regulates levels in blood
Stimulates cells to take up FA, AA and limits muscle cells to take up glucose
GROWTH HORMONE
Underproduction – dwarfism Overproduction – gigantism
THYROID-STIMULATING HORMONE
ADRENOCORTICOTROPIC HORMONE
FOLLICLE-STIMULATING HORMONE/LUTEINIZING HORMONE
MELANOCYTE-STIMULATING HORMONE Causes darkening in humans causing
the release of melanin in the skin and hair
Protects from UV rays
POSTERIOR PITUITARY GLAND Stores and releases
2 major hormones into the bloodstream Antidiuretic hormone
(vasopressin), oxytocin
These hormones are produced by the hypothalamus and stored here
ANTIDIURETIC HORMONE (VASOPRESSIN)
Causes distal convoluted tubule to become permeable to water
Helps maintain water balance
OXYTOCIN
THYROID GLAND Located in the front
of the throat and shaped like a bow tie
Secretes thyroxine (T₄),
triiodothyronine, calcitonin
THYROXINE (T₄)
Contains 4 iodine atoms
When iodine levels are low thyroid will continue to grow resulting in a goiter
CALCITONIN
Protein hormone that lowers levels of Ca²⁺ in blood
PARATHYROID GLAND 4 spherical glands (size of a pea) located
on each side of the posterior surface of the thyroid gland
Secretes Parathyroid hormone
PARATHYROID HORMONE
Stimulates enzymes in kidneys to convert vitamin D into calcitrol increasing absorption of Ca²⁺ and phosphates from food
Underproduction Muscle cramps Osteoporosis
Overproduction Kidney stones
ADRENAL GLANDS
Consist of two regions Adrenal medulla – contains
highly modified neuro-secretory neurons
Adrenal cortex – contains non-neural endocrine cells
ADRENAL MEDULLA Secretes
Epinephrine, norepinephrine These chemicals can act as hormones or
neurotransmitters (transmit nerve signals)
Part of the “fight or flight” response
EPINEPHRINE/NOREPINEPHRINE Released when body encounters stresses Epinephrine
Increase heart rate glycogen and fat breakdown Skeletal muscles, lungs blood vessels dilate
increasing blood flow Blood vessels everywhere else constrict Blood pressure raises Reduces water loss Digestive system slows Used to counter anaphylaxis
ADRENAL CORTEX Secretes
Aldosterone, cortisol
PINEAL GLAND Located near the centre of
the brain Regulates several biological
rhythms Photoreceptors in the eyes
influence pineal gland – light inhibits melatonin secretion
Helps to synchronize biological clock
Secretes melatonin
REGULATING BLOOD SUGAR Occurs automatically in
our body Pancreas – contain both
exocrine/endocrine glands
Exocrine secretes digestive
enzymes into the small intestine
Endocrine Islets of Langerhans -
Secretes insulin (beta cells) and glucagon (alpha cells)
INSULIN/GLUCAGON
Regulate the ability of most tissues in the body to metabolize fuel substances (glucose, fats, proteins)
INSULIN Secreted by beta cells Lower blood glucose levels by
Acts on skeletal muscles, liver cells, adipose tissue (fat) to uptake glucose
In the Liver Lowers fatty acid levels promotes fatty acid uptake and
storage in adipose tissue Inhibits breakdown of fats into fatty
acids Lowers amino acid levels Promotes protein synthesis Inhibits breakdown of proteins
GLUCAGON Secreted by alpha cells Increase blood glucose
levels by Stimulating breakdown of
glycogen into glucose Stimulates breakdown of
fats into fatty acids Stimulates breakdown of
proteins into amino acids Stimulate cells to use amino
acids and non-carbohydrates to synthesize glucose
GLUCOCORTICOIDS
Cortisol – Helps raise blood glucose levels using three mechanisms Stimulate synthesis of
glucose from fats and proteins
Reduce glucose uptake by the body cells except in the central nervous system
Promote breakdown of fats and proteins into fatty acids and amino acids as alternative fuels
GLUCOSE LEVELS THROUGHOUT THE DAY
UNSTABLE LEVELS OF GLUCOSE
Hyperglycemia (above 200mg/dL of blood) Blood glucose levels are too high (norm 115-200mg/dL)
Symptoms Frequent urination, sugar in the urine, vision
problems, fatigue, weight loss Hypoglycemia (below 70mg/dL of blood)
Blood glucose levels are too low (norm 70-115mg/dL)
Symptoms Nervousness, cold sweats, hunger, headaches,
weakness
DIABETES
High glucose levels in the blood caused by problems with insulin production
Symptoms Frequent urination, increased thirst, increased
appetite Classified into three different types
Type 1 Type 2 Gestational
TYPE 1 Also called juvenile diabetes or insulin-
dependant Beta cells do not produce any insulin Daily administration of insulin is required
usually by injection or pump
TYPE 2 Reduced insulin
production or the inability of insulin to bind to its receptors properly
Developed in adulthood and is associated with obesity
90% of diabetics have this type
Controlling diet and exercise helps restore normal levels of insulin production
GESTATIONAL Occurs in about 2 to
10% of pregnant women
High blood glucose levels develop during pregnancy
Usually a temporary condition but does increase the risk of both mother and child developing later in life
REPRODUCTIVE HORMONES
Gonads – sex glands Males – testes Females – ovaries
Sex hormones Androgens, estrogens,
progestins Regulate development
of male and female
reproductive systems, sexual characteristics, mating behaviour
http://www.youtube.com/watch?v=_7rsH2loIY8
FEMALE REPRODUCTIVE SYSTEM Pair of ovaries
Located in abdominal cavity Produce female gametes
(ova, eggs) Produce estrogen and
progesterone FSH and LH from the
pituitary gland stimulate the maturation of the follicles in the ovary and trigger ovulation
ESTROGEN
Estradiol Stimulates maturation of the sex organs at
puberty Development of secondary sexual
characteristics – breast development, body hair, widening of pelvis
Sex drive
PROGESTINS
Progesterone Maintains uterus for implantation of a
fertilized egg Growth and development of an embryo
OOGENESIS
Production and release of eggs (ova) by the ovaries
Releases oocytes - immature eggs that have undergone 1 meiotic division
Polar body is associated with it Disintegrates quickly
Females produce up to 1 million
Only ~380 are ovulated before menopause
OVULATION Monthly release of one or a few
developing oocytes into the oviduct
Burst of LH causes follicle to rupture
Ova becomes ovum Moves through the oviduct
(fallopian tubes) via cilia that line these tubes
Fertilization occurs here in the oviduct
undergoes second meiotic division only if penetrated by sperm cell producing a zygote
If not fertilized egg will degenerate
OVARIAN CYCLE Occurs from puberty to menopause Involves release of a mature egg approx
every 28 days Coordinated with the menstrual cycle
(month) Prepares the uterus to implant the egg if
fertilization occurs
CORPUS LUTEUM LH causes ruptured follicle to grow into an
enlarged yellowish structure Initiates luteal phase – prepares uterus to
receive an egg If egg is fertilized: Acts as an endocrine gland- secretes
estrogens, progesterone and inhibin Progesterone – inhibits GnRH – FSH LH Inhibin prevents secretion of FSH If egg is not fertilized Corpus luteum shrinks
MENSTRUAL CYCLE
Begins at day 0 Results from the breakdown of the endometrium Releases blood and tissue breakdown products
from the uterus to the outside through the vagina Day 4 or 5 – flow ceases and endometrium begins
to grow again Same hormones that control ovarian cycle control
this cycle
MENOPAUSE High levels of sex
hormones stops Late 40’s or early 50’s Menstrual/Ovarian
cycle stops Side effects
Hot flashes, headaches, mood swings
Treated with HRT (hormone replacement therapy)
MALE REPRODUCTIVE SYSTEM Testes
Affect the development of male secondary characteristics
Secrete androgens (testosterone)
Stimulates puberty, facial hair, vocal cords, sex drive
Spermatogenesis – production of sperm
Release of testosterone in the body is controlled by LH which is controlled by GnRH
SPERMATOGENESIS
Sperm development from spermatogonia Takes about 9 to 10 weeks -
spermatogonium to sperm Testes produce about 130 million fertile
sperm each day
SPERMATOGENESIS
Leydig cells - secrete testosterone
Sertoli cells – supply nutrients to spermatocytes and seal them off from body’s blood supply
Coiled seminiferous tubules located in epididymis store mature sperm
Vas deferens – transport sperm upon ejaculation