BIOLOGY PRELIMINARY NOTES
KIARA DURKIN
HUMAN ENDOCRINE SYSTEM
The nervous and endocrine systems enable animals to respond to external changes and to control
conditions inside their bodies
Chemical co-ordination
• Communication of the body by hormones
• Endocrine glands secrete hormones
• Endocrine system works with nervous system
What is a hormone?
• Organic chemical substance
• Usually a protein or steroid
• Carried to target organ(s) regulating metabolic reactions
• Hormones broken down by enzymes
What is a target organ?
• Although hormones carried in blood, they only affect certain cells with receptor sites for
hormone = target tissue/ organ
What is an endocrine gland?
• Vascular (richly supplied with blood vessels), ductless gland that secretes hormones
• Exocrine glands have ducts that carry hormones; endocrines carried in bloodstream
Endocrine glands in the body
Hypothalamus:
• Part of brain above pituitary gland
• Secretes ADH (anti-diuretic hormone)
• Role of ADH: osmoreceptors in blood vessels of hypothalamus detect increase in
osmolarity (low water levels); ADH secreted and conserves water, water reabsorbed
to blood from kidneys; less water lost in urine
Pituitary gland:
• Chemical coordinator of other endocrine glands = master gland
• Attached to hypothalamus by short stalk
• Hormones secreted by pituitary:
a) TSH (thyroid-stimulating hormone)
b) FSH (follicle-stimulating hormone) – females= stimulates ovulation in ovary;
males = stimulates spermatogenesis in testes
c) LH (luteinizing hormone) – stimulates ovulation + formation of corpus luteum
d) Prolactin – stimulates milk production in mammary glands after birth of baby
e) ACTH (adrenocorticotropic hormone) – stimulates adrenal cortex to release
hormones (cortisone + aldosterone)
f) ICSH (interstitial cell stimulating hormone) – testes secrete testosterone
, g) GH (growth hormone)/ SH (somatotrophic hormone) – promotes skeletal and
muscular growth (growth disorders: acromegaly; hyposecretion = under secretion of
hormone; hypersecretion: over secretion)
Acromegaly: adults, bones of face, hands and feet are enlarged; thickening of soft tissue =
enlarged features + tongue
Thyroid gland:
• Produce thyroxin
• Iodine required to produce thyroxin; goiter develops from low iodine levels
• Functions of thyroxin:
a) Increases basal metabolic rate (amount of energy a body needs while at rest) by
controlling rate of respiration
b) Promotes normal functioning of heart
c) Promotes normal functioning of nervous system
• Disorders:
a) Hypothyroidism (adults = myxoedema (mental and physical sluggishness, low
BP, slow heart & respiratory rate, low body heat; children = cretinism (no physical
+ sexual + mental growth & maturity)) – treated with iodine supplements;
irreversible in children
b) Hyperthyroidism (high body temp. + sweating, heart + respiratory rate & BP
increase, muscular tremors, exophthalmic goiter)
• Keeping thyroxin constant in blood:
Negative feedback system keeps hormones at a set point (pituitary detects
decrease; secretes more TSH; higher level of thyroxin inhibits release)
• Homeostasis: maintaining the set points of the body’s internal environment at their
optimal levels
• Tissue fluid = fluid that surrounds all body cells
• Homeostasis maintained through correcting deviations from the norm
• Negative feedback is made up of: receptor (detects deviation); control centre
(processes info and activates corrective mechanisms that it sends to effector);
effector (corrects change back to set point)
Pancreas:
• Exocrine & endocrine gland
• Exocrine function: secretion of pancreatic juice which flows along pancreatic duct to
duodenum where it aids digestion
• Endocrine function = secretion of hormones by cells, islets of Langerhans, directly
into blood
• Islets of Langerhans hormones: alpha cells = glucagon; beta cells = insulin
• Functions of hormones:
1. Control blood sugar levels (normal = 3.5-5.5 mmol/ liter of blood)
2. Glucose cannot enter cells without aid of insulin
3. Insulin lowers blood sugar levels; glucagon raises blood sugar levels
(antagonistic effects)
• How insulin lowers blood sugar levels
1. After consuming carbs, glucose absorbed from small intestine to blood; increases
blood sugar levels above set point; blood passes through pancreas, beta cells
detect raised levels and release insulin
KIARA DURKIN
HUMAN ENDOCRINE SYSTEM
The nervous and endocrine systems enable animals to respond to external changes and to control
conditions inside their bodies
Chemical co-ordination
• Communication of the body by hormones
• Endocrine glands secrete hormones
• Endocrine system works with nervous system
What is a hormone?
• Organic chemical substance
• Usually a protein or steroid
• Carried to target organ(s) regulating metabolic reactions
• Hormones broken down by enzymes
What is a target organ?
• Although hormones carried in blood, they only affect certain cells with receptor sites for
hormone = target tissue/ organ
What is an endocrine gland?
• Vascular (richly supplied with blood vessels), ductless gland that secretes hormones
• Exocrine glands have ducts that carry hormones; endocrines carried in bloodstream
Endocrine glands in the body
Hypothalamus:
• Part of brain above pituitary gland
• Secretes ADH (anti-diuretic hormone)
• Role of ADH: osmoreceptors in blood vessels of hypothalamus detect increase in
osmolarity (low water levels); ADH secreted and conserves water, water reabsorbed
to blood from kidneys; less water lost in urine
Pituitary gland:
• Chemical coordinator of other endocrine glands = master gland
• Attached to hypothalamus by short stalk
• Hormones secreted by pituitary:
a) TSH (thyroid-stimulating hormone)
b) FSH (follicle-stimulating hormone) – females= stimulates ovulation in ovary;
males = stimulates spermatogenesis in testes
c) LH (luteinizing hormone) – stimulates ovulation + formation of corpus luteum
d) Prolactin – stimulates milk production in mammary glands after birth of baby
e) ACTH (adrenocorticotropic hormone) – stimulates adrenal cortex to release
hormones (cortisone + aldosterone)
f) ICSH (interstitial cell stimulating hormone) – testes secrete testosterone
, g) GH (growth hormone)/ SH (somatotrophic hormone) – promotes skeletal and
muscular growth (growth disorders: acromegaly; hyposecretion = under secretion of
hormone; hypersecretion: over secretion)
Acromegaly: adults, bones of face, hands and feet are enlarged; thickening of soft tissue =
enlarged features + tongue
Thyroid gland:
• Produce thyroxin
• Iodine required to produce thyroxin; goiter develops from low iodine levels
• Functions of thyroxin:
a) Increases basal metabolic rate (amount of energy a body needs while at rest) by
controlling rate of respiration
b) Promotes normal functioning of heart
c) Promotes normal functioning of nervous system
• Disorders:
a) Hypothyroidism (adults = myxoedema (mental and physical sluggishness, low
BP, slow heart & respiratory rate, low body heat; children = cretinism (no physical
+ sexual + mental growth & maturity)) – treated with iodine supplements;
irreversible in children
b) Hyperthyroidism (high body temp. + sweating, heart + respiratory rate & BP
increase, muscular tremors, exophthalmic goiter)
• Keeping thyroxin constant in blood:
Negative feedback system keeps hormones at a set point (pituitary detects
decrease; secretes more TSH; higher level of thyroxin inhibits release)
• Homeostasis: maintaining the set points of the body’s internal environment at their
optimal levels
• Tissue fluid = fluid that surrounds all body cells
• Homeostasis maintained through correcting deviations from the norm
• Negative feedback is made up of: receptor (detects deviation); control centre
(processes info and activates corrective mechanisms that it sends to effector);
effector (corrects change back to set point)
Pancreas:
• Exocrine & endocrine gland
• Exocrine function: secretion of pancreatic juice which flows along pancreatic duct to
duodenum where it aids digestion
• Endocrine function = secretion of hormones by cells, islets of Langerhans, directly
into blood
• Islets of Langerhans hormones: alpha cells = glucagon; beta cells = insulin
• Functions of hormones:
1. Control blood sugar levels (normal = 3.5-5.5 mmol/ liter of blood)
2. Glucose cannot enter cells without aid of insulin
3. Insulin lowers blood sugar levels; glucagon raises blood sugar levels
(antagonistic effects)
• How insulin lowers blood sugar levels
1. After consuming carbs, glucose absorbed from small intestine to blood; increases
blood sugar levels above set point; blood passes through pancreas, beta cells
detect raised levels and release insulin
