HUMAN ENDOCRINE SYSTEM – SUMMARY
Purpose of the Endocrine System
⁃ The body must keep a constant internal balance known as homeostasis,
despite external/internal environmental changes.
⁃ Nervous system & hormones enable animals to respond to external changes
& to control conditions inside their bodies.
⁃ Endocrine system consists of endocrine glands which secrete organic
compounds, chemical messengers called hormones.
Endocrine Glands vs Exocrine Glands
⁃ Endocrine glands: Ductless, secrete hormones directly into bloodstream.
Blood transports hormones to target organs, where they perform their function.
⁃ Exocrine glands: Use ducts to release secretions to body cavities.
⁃ Endocrine glands don’t work alone – they interact to control almost all
metabolic activities.
Hormones
⁃ Organic chemical messengers. Most are proteins, some are steroids
(lipid-like organic compounds).
⁃ Secreted in small quantities by endocrine glands directly into blood.
⁃ Transported to target organs via bloodstream.
⁃ Target organ = organ with receptors for a specific hormone, so it can
respond.
⁃ Have regulatory function– can be stimulating or inhibiting.
⁃ Can be regulated by negative or positive feedback mechanisms.
Negative Feedback Mechanism
⁃ Deviation from normal levels (of substance/temperature) triggers a
response that restores normal levels.
Endocrine Glands And Their Hormones:
1. Hypothalamus
2. pituitary/hypophysis
3. thyroid
4. adrenal glands
5. pancreas
6. ovary (F), testis (M)
Hypophysis/Pituitary Gland – “Master Gland”
⁃ called master gland: secretes many hormones that affect many other
endocrine glands.
⁃ Located at base of brain, attached to hypothalamus by a short stalk.
Fits into a small bony cavity in the cranium.
⁃ Part of the brain located just below corpus callousness, controls
functions of hypophysis.
⁃ link between nervous + endocrine systems.
⁃ 2 lobes:
⁃ Anterior lobe (adenohypophysis)
⁃ Posterior lobe (neurohypophysis)
Relationship Between The Hypothalamus and The Hypophysis:
Hypothalamus connected to hypophysis in 2 ways:
⁃ Blood vessels to anterior lobe
⁃ Neurons to posterior lobe
⁃ Hypothalamus makes hormones like ADH → stored in posterior lobe.
⁃ Hypothalamus sends releasing factors via blood/neurons, stimulating the
hypophysis to produce &/or release hormones into the blood.
⁃
Hormones of Anterior Lobe
, ⁃ TSH (Thyroid Stimulating Hormone): Stimulates thyroid to secrete
hormone thyroxin.
⁃ Growth Hormone (STH/Somatotropic hormone): Promotes growth of skeleton
+ muscles by stimulating protein synthesis.
⁃ Growth Disorders from GH:
Abnormalities caused by abnormal secretion of GH:
⁃ Hyposecretion = under-secretion Hypersecretion = over-secretion
⁃ Dwarfism: Under-secretion in children → very short body, proportional
body parts, normal mental ability, doesn’t reach sexual maturity.
⁃ NB: in genetic dwarfism = body parts out of proportion (e.g normal
sized head & torso with short arms & legs)
⁃ Gigantism: Over-secretion in children → usually from pituitary tumour.
⁃ Acromegaly: Over-secretion in adults → long bones have completed
growth, therefore can’t lengthen anymore, growth plates in the epiphyses of long
bones close during puberty, so bones in the face/jaw, hands, feet enlarge.
⁃ FSH (Follicle-Stimulating Hormone):
⁃ Females: Stimulates development of primary follicles → to a mature
Graafian follicles in ovary.
⁃ Males: Activates germinal epithelium → sperm production in testes.
⁃ LH (Luteinising Hormone):
⁃ Females: Stimulates ovulation + development of corpus luteum in the
ovary.
⁃ Males: Stimulates Leydig cells → to produce testosterone in the testes.
⁃ Prolactin:
⁃ Stimulates mammary glands to produce milk after birth.
Hormones of the Posterior Lobe
⁃ ADH (Antidiuretic Hormone) = anti-dehydration hormone :Thus prevents
dehydration
⁃ Produced by hypothalamus, transported via neurons to posterior lobe for
storage.
⁃ When volume of water ↓ in the blood, osmoreceptors in hypothalamus
detect the change → stimulate the neurons (that connect the hypothalamus to thy
hypophysis), in posterior lobe of hypophysis to release stored ADH.
⁃ Function: controls the reabsorption of water by making the walls of
renal tubules + collecting ducts more permeable to water → thus more water is
reabsorbed, less water exerted with urine → helps conserve water in the body.
⁃ Oxytocin:
⁃ Produced in hypothalamus, released by posterior lobe of the hypophysis.
⁃ Causes uterine contractions necessary for birth, which stimulate the
hypophysis to release more oxytocin.
⁃ A positive feedback example: Uterine contractions → more oxytocin
released → more contractions. Continues until baby is born.
⁃ Thyroid Gland
⁃ Location: 2 lobes on either side of trachea, below the larynx.
⁃ Hormone: Produces & secretes hormone thyroxin. Iodine is essential for
thyroxin production. Iodine shortage → can cause thyroid to enlarge which is known
as simple goitre.
⁃ Functions of Thyroxin:
⁃ Increases basal metabolic rate (among of energy body needs to function
when at rest)
⁃ Increases breathing rate + heart rate.
⁃ Essential for normal growth/development of organs and for normal
Purpose of the Endocrine System
⁃ The body must keep a constant internal balance known as homeostasis,
despite external/internal environmental changes.
⁃ Nervous system & hormones enable animals to respond to external changes
& to control conditions inside their bodies.
⁃ Endocrine system consists of endocrine glands which secrete organic
compounds, chemical messengers called hormones.
Endocrine Glands vs Exocrine Glands
⁃ Endocrine glands: Ductless, secrete hormones directly into bloodstream.
Blood transports hormones to target organs, where they perform their function.
⁃ Exocrine glands: Use ducts to release secretions to body cavities.
⁃ Endocrine glands don’t work alone – they interact to control almost all
metabolic activities.
Hormones
⁃ Organic chemical messengers. Most are proteins, some are steroids
(lipid-like organic compounds).
⁃ Secreted in small quantities by endocrine glands directly into blood.
⁃ Transported to target organs via bloodstream.
⁃ Target organ = organ with receptors for a specific hormone, so it can
respond.
⁃ Have regulatory function– can be stimulating or inhibiting.
⁃ Can be regulated by negative or positive feedback mechanisms.
Negative Feedback Mechanism
⁃ Deviation from normal levels (of substance/temperature) triggers a
response that restores normal levels.
Endocrine Glands And Their Hormones:
1. Hypothalamus
2. pituitary/hypophysis
3. thyroid
4. adrenal glands
5. pancreas
6. ovary (F), testis (M)
Hypophysis/Pituitary Gland – “Master Gland”
⁃ called master gland: secretes many hormones that affect many other
endocrine glands.
⁃ Located at base of brain, attached to hypothalamus by a short stalk.
Fits into a small bony cavity in the cranium.
⁃ Part of the brain located just below corpus callousness, controls
functions of hypophysis.
⁃ link between nervous + endocrine systems.
⁃ 2 lobes:
⁃ Anterior lobe (adenohypophysis)
⁃ Posterior lobe (neurohypophysis)
Relationship Between The Hypothalamus and The Hypophysis:
Hypothalamus connected to hypophysis in 2 ways:
⁃ Blood vessels to anterior lobe
⁃ Neurons to posterior lobe
⁃ Hypothalamus makes hormones like ADH → stored in posterior lobe.
⁃ Hypothalamus sends releasing factors via blood/neurons, stimulating the
hypophysis to produce &/or release hormones into the blood.
⁃
Hormones of Anterior Lobe
, ⁃ TSH (Thyroid Stimulating Hormone): Stimulates thyroid to secrete
hormone thyroxin.
⁃ Growth Hormone (STH/Somatotropic hormone): Promotes growth of skeleton
+ muscles by stimulating protein synthesis.
⁃ Growth Disorders from GH:
Abnormalities caused by abnormal secretion of GH:
⁃ Hyposecretion = under-secretion Hypersecretion = over-secretion
⁃ Dwarfism: Under-secretion in children → very short body, proportional
body parts, normal mental ability, doesn’t reach sexual maturity.
⁃ NB: in genetic dwarfism = body parts out of proportion (e.g normal
sized head & torso with short arms & legs)
⁃ Gigantism: Over-secretion in children → usually from pituitary tumour.
⁃ Acromegaly: Over-secretion in adults → long bones have completed
growth, therefore can’t lengthen anymore, growth plates in the epiphyses of long
bones close during puberty, so bones in the face/jaw, hands, feet enlarge.
⁃ FSH (Follicle-Stimulating Hormone):
⁃ Females: Stimulates development of primary follicles → to a mature
Graafian follicles in ovary.
⁃ Males: Activates germinal epithelium → sperm production in testes.
⁃ LH (Luteinising Hormone):
⁃ Females: Stimulates ovulation + development of corpus luteum in the
ovary.
⁃ Males: Stimulates Leydig cells → to produce testosterone in the testes.
⁃ Prolactin:
⁃ Stimulates mammary glands to produce milk after birth.
Hormones of the Posterior Lobe
⁃ ADH (Antidiuretic Hormone) = anti-dehydration hormone :Thus prevents
dehydration
⁃ Produced by hypothalamus, transported via neurons to posterior lobe for
storage.
⁃ When volume of water ↓ in the blood, osmoreceptors in hypothalamus
detect the change → stimulate the neurons (that connect the hypothalamus to thy
hypophysis), in posterior lobe of hypophysis to release stored ADH.
⁃ Function: controls the reabsorption of water by making the walls of
renal tubules + collecting ducts more permeable to water → thus more water is
reabsorbed, less water exerted with urine → helps conserve water in the body.
⁃ Oxytocin:
⁃ Produced in hypothalamus, released by posterior lobe of the hypophysis.
⁃ Causes uterine contractions necessary for birth, which stimulate the
hypophysis to release more oxytocin.
⁃ A positive feedback example: Uterine contractions → more oxytocin
released → more contractions. Continues until baby is born.
⁃ Thyroid Gland
⁃ Location: 2 lobes on either side of trachea, below the larynx.
⁃ Hormone: Produces & secretes hormone thyroxin. Iodine is essential for
thyroxin production. Iodine shortage → can cause thyroid to enlarge which is known
as simple goitre.
⁃ Functions of Thyroxin:
⁃ Increases basal metabolic rate (among of energy body needs to function
when at rest)
⁃ Increases breathing rate + heart rate.
⁃ Essential for normal growth/development of organs and for normal
