Endocrine System
Endocrine system overview
Two systems in your body secrete organic compounds
- Endocrine system: series of ductless glands which secrete
hormones directly into the blood
o Eg: pituitary gland
- Exocrine system: series of glands which release secretions
into ducts into a body cavity
o Eg: saliva glands
The endocrine glands secrete organic chemical messengers known as
hormones
- The glands interact continuously to maintain homeostasis
o Homeostasis is the maintenance of a "dynamic
equilibrium" in the body despite changes to the
internal or external environment
- The control and coordination hormones bring is known as “chemical coordination”
Hormones play a regulatory function in the body
- They stimulate or inhibit the production of other hormones or chemical compounds
- They are transported in small quantities through the bloodstream to target organs
Hormones are regulated by positive or negative feedback loops
- Positive feedback: does not regulate homeostasis but amplifies the response to hormone
o Eg: oxytocin during labour makes contractions come faster and stronger
- Negative feedback: a change in homeostasis stimulates a response to return to homeostasis
o Eg: progesterone inhibits the production of FSH
Hormones can be protein-based, lipid-based (end “-ol” or “-one”) or amines ( end “-ine”)
- Protein-based hormones bind to receptors on the cell membrane
o They are hydrophilic
o They can be polypeptides (small) or glycoproteins (large carbohydrates)
- Lipid-based hormones (steroids) bind to a cell nucleus and activate genes
o They are hydrophobic
o They are derived from cholesterol
- Amines share qualities of both protein and lipid-based hormones but are small molecules
o They are modified amino acids
, Endocrine System
Pituitary Gland/Hypophysis
Located at the base of the brain and attached to the hypothalamus
- Hypothalamus controls the functions of the hypophysis
- The hypothalamus forms the link between the nervous and endocrine systems
The hypophysis consists of 2 lobes
- Anterior lobe is the adenohypophysis and has lots of
capillaries to secrete hormones
- Posterior lobe is the neurohypophysis and has nerve
fibres which receive stimulus from the hypothalamus
Hormones of the anterior lobe
- Thyroid-stimulating hormone (TSH)
o Stimulates the thyroid to secrete thyroxin
- Growth hormone (STH/somatotropic hormone) –
Peptide
o Promotes the growth of the skeleton and muscles by stimulating protein synthesis
o Undersecretion causes pituitary dwarfism
Individuals do not reach sexual maturity or develop secondary sex
characteristics
o Oversecretion in children causes gigantism
o Oversecretion in adults causes acromegaly
Long bones do not lengthen but others do so facial bones, and bones of the
hands and feet increase in size
- Follicle-stimulating hormone (FSH) – glycoprotein
o Stimulates the development of primary follicles to Graafian follicles in the ovaries
o Activates the germinal epithelium which produces sperm
- Luteinising hormone (LH) – glycoprotein
o Stimulates ovulation and development of the corpus luteum
o Stimulates the cells of Leydig to produce testosterone
- Prolactin
o Stimulates the mammary glands to produce milk
Hormones of the posterior lobe
- Antidiuretic hormone (ADH) – polypeptide
o Produced by the hypothalamus and stored and released by the posterior pituitary
o Controls the permeability of renal tubules for osmoregulation
- Oxytocin
o Produced by the hypothalamus and stored and released by the posterior pituitary
Endocrine system overview
Two systems in your body secrete organic compounds
- Endocrine system: series of ductless glands which secrete
hormones directly into the blood
o Eg: pituitary gland
- Exocrine system: series of glands which release secretions
into ducts into a body cavity
o Eg: saliva glands
The endocrine glands secrete organic chemical messengers known as
hormones
- The glands interact continuously to maintain homeostasis
o Homeostasis is the maintenance of a "dynamic
equilibrium" in the body despite changes to the
internal or external environment
- The control and coordination hormones bring is known as “chemical coordination”
Hormones play a regulatory function in the body
- They stimulate or inhibit the production of other hormones or chemical compounds
- They are transported in small quantities through the bloodstream to target organs
Hormones are regulated by positive or negative feedback loops
- Positive feedback: does not regulate homeostasis but amplifies the response to hormone
o Eg: oxytocin during labour makes contractions come faster and stronger
- Negative feedback: a change in homeostasis stimulates a response to return to homeostasis
o Eg: progesterone inhibits the production of FSH
Hormones can be protein-based, lipid-based (end “-ol” or “-one”) or amines ( end “-ine”)
- Protein-based hormones bind to receptors on the cell membrane
o They are hydrophilic
o They can be polypeptides (small) or glycoproteins (large carbohydrates)
- Lipid-based hormones (steroids) bind to a cell nucleus and activate genes
o They are hydrophobic
o They are derived from cholesterol
- Amines share qualities of both protein and lipid-based hormones but are small molecules
o They are modified amino acids
, Endocrine System
Pituitary Gland/Hypophysis
Located at the base of the brain and attached to the hypothalamus
- Hypothalamus controls the functions of the hypophysis
- The hypothalamus forms the link between the nervous and endocrine systems
The hypophysis consists of 2 lobes
- Anterior lobe is the adenohypophysis and has lots of
capillaries to secrete hormones
- Posterior lobe is the neurohypophysis and has nerve
fibres which receive stimulus from the hypothalamus
Hormones of the anterior lobe
- Thyroid-stimulating hormone (TSH)
o Stimulates the thyroid to secrete thyroxin
- Growth hormone (STH/somatotropic hormone) –
Peptide
o Promotes the growth of the skeleton and muscles by stimulating protein synthesis
o Undersecretion causes pituitary dwarfism
Individuals do not reach sexual maturity or develop secondary sex
characteristics
o Oversecretion in children causes gigantism
o Oversecretion in adults causes acromegaly
Long bones do not lengthen but others do so facial bones, and bones of the
hands and feet increase in size
- Follicle-stimulating hormone (FSH) – glycoprotein
o Stimulates the development of primary follicles to Graafian follicles in the ovaries
o Activates the germinal epithelium which produces sperm
- Luteinising hormone (LH) – glycoprotein
o Stimulates ovulation and development of the corpus luteum
o Stimulates the cells of Leydig to produce testosterone
- Prolactin
o Stimulates the mammary glands to produce milk
Hormones of the posterior lobe
- Antidiuretic hormone (ADH) – polypeptide
o Produced by the hypothalamus and stored and released by the posterior pituitary
o Controls the permeability of renal tubules for osmoregulation
- Oxytocin
o Produced by the hypothalamus and stored and released by the posterior pituitary
