Endocrine System

Hormone

Chemical substance (protein or steroid) transported in blood to target organs where it regulates metabolic reactions

Endocrine gland

Ductless gland that releases hormones directly into blood via capillaries

Exocrine gland

Gland with ducts that releases secretions into a cavity, e.g. salivary glands

Pancreas - exocrine function

Produces digestive enzymes released via pancreatic duct into duodenum

Pancreas - endocrine function

Releases insulin and glucagon directly into the blood

Homeostasis

Maintenance of a relatively constant internal environment despite changes in the external environment

Negative feedback

A disturbance triggers a response that counteracts it and restores the system to its original state

Positive feedback

The output enhances (rather than reduces) the original stimulus

Example of positive feedback

Childbirth - oxytocin intensifies contractions, which triggers more oxytocin release, until birth

Hypothalamus

Part of brain above pituitary; links nervous and endocrine systems by controlling pituitary hormone release

ADH (antidiuretic hormone)

Made in hypothalamus, released by pituitary; makes kidney collecting ducts more permeable so more water is reabsorbed

Oxytocin (general)

Made in hypothalamus, released by pituitary; stimulates uterine contractions and milk release after birth

GnRH

Gonadotropin releasing hormone; controls release of LH and FSH

Pituitary gland

The "master gland" of the body; attached to hypothalamus by a short stalk

TSH

Stimulates the thyroid gland to secrete thyroxine

FSH - general action

Targets reproductive organ cells to undergo meiosis and form gametes

LH - general action

Targets cells in testes (males) and ovaries (females)

GH (growth hormone)

Targets skeleton and muscles to promote growth by stimulating protein synthesis

Prolactin - general action

Stimulates milk production in mammary glands

Thyroid gland

Butterfly-shaped gland at base of neck; releases thyroxine which regulates metabolism

Iodine's role

Required for thyroxine production; deficiency can cause a goitre

Goitre

Enlargement of the thyroid gland caused by iodine deficiency

Basal metabolic rate

Amount of energy needed to maintain body functions at rest

Functions of thyroxine

Increases basal metabolic rate/body heat; promotes normal heart function; supports nervous system alertness/reflexes

Adrenal glands

Located on top of the kidneys; each made of outer cortex and inner medulla

Aldosterone

Secreted by adrenal cortex; increases sodium ion reabsorption in kidney nephrons

Cortisol

Secreted by adrenal cortex; increases body's ability to resist stress long-term

Adrenalin (epinephrine)

Secreted by adrenal medulla; the "fight or flight" hormone released under sudden danger/stress

Effects of adrenalin

Increases heart rate, breathing rate, muscle tone, blood sugar, alertness, sweating; shifts blood to muscles/skin; decreases gut peristalsis; dilates pupils; promotes urination

Islets of Langerhans

Groups of pancreas cells that secrete hormones directly into the bloodstream

Alpha cells

Pancreas cells that produce glucagon

Beta cells

Pancreas cells that produce insulin

Glucagon's action

Stimulates liver cells to convert stored glycogen into glucose, raising blood glucose

Insulin's action

Promotes glucose uptake into cells and storage as glycogen, lowering blood glucose

When is glucagon released

When blood glucose falls below normal

When is insulin released

When blood glucose rises above normal (e.g. after a meal)

Gonads

Testes (males) and ovaries (females); secrete sex hormones

Oestrogen - functions

Increases puberty growth rate; causes secondary sexual characteristics; matures reproductive organs; prepares endometrium for pregnancy; high levels inhibit FSH/LH

Progesterone - functions

Works with oestrogen on endometrium changes; maintains endometrium during pregnancy; keeps uterine smooth muscle relaxed in pregnancy

Testosterone - functions

Increases puberty growth rate; causes secondary sexual characteristics; matures reproductive organs; increases sex drive; promotes gamete production

Gigantism

Hypersecretion of GH before puberty; overdevelopment of the skeleton

Acromegaly

Hypersecretion of GH after puberty; enlargement of bones of face/hands/feet and thickened soft tissue

Cause of gigantism and acromegaly

Usually a noncancerous pituitary tumour (adenoma)

Pituitary dwarfism

Hyposecretion of GH in children; underdeveloped skeleton, normal proportions and cognition

Treatment for pituitary dwarfism

GH injections manufactured by genetically engineered bacteria

Myxoedema

Hypothyroidism in adults; mental/physical sluggishness, low blood pressure, low heart/respiratory rate, low body temperature

Cretinism

Hypothyroidism in children; decreased physical growth, immature sexual development, impaired cognitive function

Grave's disease

Example of hyperthyroidism; too much thyroxine causes high metabolic rate, raised temperature/sweating, raised heart/respiratory rate, tremors, nervousness

Diabetes

Inability to control blood glucose levels; characterised by high blood glucose

Type 1 diabetes

Pancreas produces little/no insulin; often autoimmune; no cure, requires insulin

Type 2 diabetes

Body's cells become insulin resistant; linked to obesity/inactivity; managed with lifestyle changes

Hormones important for athletic performance

Testosterone (muscle/strength), growth hormone (muscle repair), cortisol (stress response), thyroid hormones (metabolism), insulin (blood sugar), oestrogen (bone health)

Doping

Consuming artificial/illegal substances (e.g. anabolic steroids, hGH) for competitive advantage

Anabolic steroids

Substances similar in structure to testosterone that help build muscle

Male reproductive system parts

Testes (primary sex organ), ducts, accessory glands, penis (external genitalia)

Testis function

Sperm production, in seminiferous tubules

Epididymis function

Sperm transport, maturation and storage

Vas deferens function

Sperm transport and ejaculation

Seminal vesicles function

Secrete alkaline, fructose-rich liquid to transport sperm

Prostate gland function

Secretes alkaline solution to neutralise urine and the acidic female tract

Cowper's gland function

Secretes fluid that lubricates and flushes out residual urine

Urethra function (male)

Passage for urine and sperm

Penis function

Organ of copulation (intromission)

Vasectomy

Surgical sterilisation in males by cutting/tying the vas deferens

Scrotum function

Sac that regulates testes temperature at about 34°C, vital for sperm production

Spermatogenesis

Process by which seminiferous tubules produce sperm

Where is testosterone produced

Interstitial (Leydig) tissue of the testes, under influence of LH

Sperm structure - 3 parts

Head (haploid nucleus + acrosome), midpiece (mitochondria), tail/flagellum (propulsion)

Acrosome function

Contains digestive enzymes that break down the zona pellucida to enter the egg

Semen composition

Sperm plus secretions of prostate gland, Cowper's glands, and seminal vesicles

Epididymis maturation time

1 to 10 days; sperm can be stored up to 4 weeks before reabsorption

Female reproductive system parts

Ovaries (primary sex organs); fallopian tubes, uterus, vagina (accessory organs); vulva (external genitalia)

Ovary function

Site of oogenesis; produces oestrogen and progesterone

Fallopian tube (oviduct) function

Transports ova from ovary to uterus; usual site of fertilisation

Fimbriae function

Finger-like projections that sweep the released ovum into the oviduct

Uterus function

Site of implantation, foetal development, and origin of labour contractions

Myometrium

Muscular wall layer of the uterus; responsible for labour contractions

Endometrium

Lining of the uterus; vascular layer shed during menstruation

Cervix function

Connects uterus to vagina; makes mucus that changes across the cycle; dilates during childbirth

Vagina function

Passage for menstrual flow, receptacle for penis during coitus, lower birth canal

Clitoris

Contains erectile tissue and nerves; homologous to the glans penis; role in sexual excitation

Hymen

Thin membrane fold that partially closes the vaginal orifice

Primary follicle

Ovarian structure containing an immature egg; number determined at birth

Graafian follicle

Mature follicle that secretes oestrogen and releases the ovum at ovulation

Corpus luteum

Structure formed from the follicle after ovulation; secretes oestrogen and progesterone

Puberty onset - girls

Usually between 11 and 14 years

Puberty onset - boys

Usually between 13 and 15 years

Gametogenesis

Formation of mature gametes (sperm/eggs) by the gonads via meiosis

Oogenesis

Production of haploid mature eggs in ovarian follicles

Oogenesis vs spermatogenesis differences

Egg number set before birth; eggs not formed continuously; occurs in a monthly cycle

Menstrual cycle phases in order

Menstrual phase, follicular phase, ovulation phase, luteal phase

Average menstrual cycle length

28 days

Menstrual phase

Day 1; uterine lining sheds because oestrogen and progesterone drop after an unfertilised egg

Follicular phase

Day 1 to about day 14; FSH stimulates development of follicles in the ovary

Ovulation phase

Around day 14; LH surge triggers release of a mature egg; lasts about 24 hours

Luteal phase

After ovulation; follicle becomes corpus luteum, releasing progesterone (and some oestrogen) to maintain the uterine lining

hCG

Human chorionic gonadotropin; detected by pregnancy tests; maintains the corpus luteum if pregnancy occurs

FSH role in menstrual cycle

Released by pituitary; stimulates development of the Graafian follicle

LH role in menstrual cycle

Released by pituitary; triggers ovulation and stimulates corpus luteum development

Oestrogen role in menstrual cycle

Released by follicle/corpus luteum; repairs uterine lining and stimulates female sexual characteristics