Physiology
Medical physiology for MBBS: cell and body fluids, blood, nerve and muscle, and the cardiovascular, respiratory, gastrointestinal, renal, endocrine, reproductive and nervous systems, special senses and integrative physiology.
12chapters144questions84High-Yield
Definition
Male reproduction involves spermatogenesis (sperm formation in the testis) and testosterone secretion, under hypothalamo-pituitary control.
Spermatogenesis
- Occurs in the seminiferous tubules
- Spermatogonia → primary → secondary spermatocyte → spermatid → sperm
- Takes ~64–74 days
- Needs testosterone, FSH, cool scrotal temperature
Testosterone (Leydig cells)
- Male secondary sexual characters
- Supports spermatogenesis and libido
- Anabolic (muscle, bone)
Hormonal Control
- Hypothalamus (GnRH) → pituitary (FSH, LH)
- LH → Leydig cells → testosterone
- FSH → Sertoli cells → spermatogenesis
GnRH drives FSH/LH, which drive sperm production and testosterone. Hormone Target Effect LH Leydig cells Testosterone FSH Sertoli cells Spermatogenesis Testosterone Body Sex characters Applied
- Cryptorchidism → infertility
- Vasectomy — male contraception
🔑KEY POINTS TO REMEMBER- Spermatogenesis in seminiferous tubules (~64–74 days).
- LH → testosterone (Leydig); FSH → spermatogenesis (Sertoli).
- Needs cool scrotal temperature.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
Female reproduction involves oogenesis (ovum formation) and the ovarian cycle (follicular → ovulation → luteal), controlled by FSH and LH.
Oogenesis
- Begins in fetal life, then arrested
- Primary oocyte → (at ovulation) secondary oocyte
- Completed only if fertilised
- Far fewer ova than sperm
Ovarian Cycle
- Follicular phase — follicle matures (FSH, oestrogen)
- Ovulation — LH surge releases the ovum
- Luteal phase — corpus luteum (progesterone)
Hormones
- Oestrogen — follicle growth, endometrial proliferation
- Progesterone — secretory endometrium
- FSH/LH — pituitary control
The ovary cycles through follicle growth, ovulation and the corpus luteum. Phase Hormone Event Follicular Oestrogen Follicle grows Ovulation LH surge Ovum released Luteal Progesterone Corpus luteum Applied
- PCOS — anovulation
- Basis of hormonal contraception
🔑KEY POINTS TO REMEMBER- Oogenesis arrested until ovulation; completed if fertilised.
- Ovarian cycle: follicular → ovulation (LH surge) → luteal.
- Oestrogen (proliferative) & progesterone (secretory).
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
The menstrual cycle is the ~28-day cyclical change in the ovary and endometrium preparing for pregnancy, controlled by ovarian and pituitary hormones.
Endometrial Phases
- Menstrual (1–5) — shedding of the endometrium
- Proliferative (6–14) — oestrogen → endometrium grows
- Secretory (15–28) — progesterone → secretory endometrium
Hormonal Events
- FSH → follicle → oestrogen
- LH surge → ovulation (~day 14)
- Corpus luteum → progesterone
- No pregnancy → corpus luteum regresses → menstruation
The endometrium sheds, grows, then becomes secretory — driven by ovarian hormones. Phase Days Hormone Menstrual 1–5 ↓ all Proliferative 6–14 Oestrogen Ovulation 14 LH surge Secretory 15–28 Progesterone Applied
- Fertile period around day 14
- Amenorrhoea, dysmenorrhoea
🔑KEY POINTS TO REMEMBER- Endometrial phases: menstrual, proliferative (oestrogen), secretory (progesterone).
- Ovulation ~day 14 (LH surge).
- Corpus luteum regresses → menstruation if no pregnancy.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
Pregnancy follows fertilisation and implantation; the placenta supports the fetus, and parturition is childbirth.
Fertilisation & Implantation
- Fertilisation in the fallopian tube
- Zygote → blastocyst → implants in endometrium (~day 7)
- hCG maintains the corpus luteum
Placenta
- A fetomaternal organ
- Functions: nutrition, gas exchange, excretion, hormones, barrier
Parturition
- Positive feedback: oxytocin + prostaglandins
- Cervical stretch → ↑ oxytocin → contractions
- Three stages of labour
From fertilisation to birth: implantation, placental support, then labour. Structure Role Placenta Nutrition, gas, hormones hCG Maintains corpus luteum Oxytocin Labour contractions Applied
- Pregnancy test detects hCG
- Placenta praevia, abruption
🔑KEY POINTS TO REMEMBER- Fertilisation in tube; implantation ~day 7; hCG maintains corpus luteum.
- Placenta: nutrition, gas, excretion, hormones, barrier.
- Parturition driven by oxytocin (positive feedback).
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
Lactation is milk production and ejection after childbirth; puberty is the transition to reproductive maturity.
Lactation
- Prolactin → milk secretion
- Oxytocin → milk ejection (let-down)
- Suckling maintains both (neuroendocrine reflex)
- Colostrum provides antibodies (IgA)
Puberty
- Onset by GnRH → FSH/LH → gonadal hormones
- Girls: menarche, breast development
- Boys: spermatogenesis, deepening voice
- Growth spurt
Suckling drives prolactin (make milk) and oxytocin (eject milk). Hormone Role in lactation Prolactin Milk secretion Oxytocin Milk ejection Applied
- Breastfeeding delays ovulation
- Precocious or delayed puberty
🔑KEY POINTS TO REMEMBER- Lactation: prolactin (secretion) + oxytocin (ejection); colostrum = IgA.
- Puberty triggered by GnRH → FSH/LH → gonadal hormones.
- Breastfeeding delays ovulation.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
Spermatogenesis is the formation of mature sperm from spermatogonia in the seminiferous tubules of the testis.
Stages
- Spermatogonia (2n)
- → primary spermatocyte (2n)
- → secondary spermatocyte (n) [meiosis I]
- → spermatid → spermatozoa [meiosis II + spermiogenesis]
Requirements
- Testosterone and FSH
- Sertoli cell support
- Cool temperature (~2°C below body)
Two meiotic divisions turn a diploid spermatogonium into haploid sperm. Cell Ploidy Spermatogonium 2n Primary spermatocyte 2n Secondary spermatocyte n Spermatozoon n Applied
- Takes ~64–74 days
- Heat / varicocele → impaired sperm production
🔑KEY POINTS TO REMEMBER- Spermatogenesis in seminiferous tubules; needs testosterone, FSH, cool temp.
- Spermatogonium (2n) → spermatozoon (n) via meiosis.
- Takes ~64–74 days.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
Testosterone is the main male sex hormone, secreted by Leydig cells under LH control.
Functions
- Male secondary sexual characters
- Spermatogenesis and libido
- Anabolic — muscle and bone growth
- Male pattern hair, deep voice
Regulation
- LH → Leydig cells → testosterone
- Negative feedback on GnRH/LH
LH drives Leydig-cell testosterone, which feeds back to control its own level. Effect Example Sexual Sex characters, libido Anabolic Muscle, bone Reproductive Spermatogenesis Applied
- Anabolic steroid abuse
- Hypogonadism
🔑KEY POINTS TO REMEMBER- Testosterone from Leydig cells under LH.
- Sexual, anabolic and reproductive effects.
- Negative feedback on GnRH/LH.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
Ovulation is the release of a secondary oocyte from the mature ovarian follicle, triggered by the LH surge (~day 14).
Mechanism
- Oestrogen peak → LH surge (positive feedback)
- LH → follicle rupture → ovum released
- Remaining follicle → corpus luteum
Signs
- Mid-cycle rise in basal body temperature
- Mittelschmerz (mid-cycle pain)
- Cervical mucus becomes thin, stretchy
A high oestrogen level triggers the LH surge that ruptures the follicle. Event Timing LH surge ~Day 14 Ovulation ~Day 14 Fertile window Days 10–16 Applied
- Basis of fertility timing
- Ovulation induction (clomiphene)
🔑KEY POINTS TO REMEMBER- Ovulation ~day 14, triggered by the LH surge (positive feedback).
- Signs: ↑ BBT, mittelschmerz, mucus change.
- Follicle → corpus luteum after ovulation.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
Human chorionic gonadotropin (hCG) is a hormone from the placenta (syncytiotrophoblast) that maintains the corpus luteum in early pregnancy.
Functions
- Maintains the corpus luteum → progesterone
- Prevents menstruation; supports early pregnancy
- Basis of pregnancy tests
Timeline
- Detectable ~day 8–10 after fertilisation
- Peaks ~10 weeks, then falls
hCG keeps the corpus luteum alive so progesterone sustains the pregnancy. Feature Detail Source Placenta (syncytiotrophoblast) Action Maintains corpus luteum Use Pregnancy test Applied
- Urine/blood pregnancy test
- ↑ in molar pregnancy and some tumours
🔑KEY POINTS TO REMEMBER- hCG from placenta maintains the corpus luteum.
- Detectable ~day 8–10; basis of pregnancy tests.
- ↑ in molar pregnancy.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
The corpus luteum is the endocrine structure formed from the ruptured follicle after ovulation, secreting mainly progesterone.
Functions
- Secretes progesterone (and some oestrogen)
- Maintains the secretory endometrium
- Supports early pregnancy
Fate
- No pregnancy → regresses (corpus albicans) in ~12 days → menstruation
- Pregnancy → maintained by hCG
The corpus luteum makes progesterone, then either regresses or is rescued by hCG. Outcome Fate of corpus luteum No pregnancy Regresses → menstruation Pregnancy Maintained by hCG Applied
- Progesterone support in early pregnancy
- Luteal phase defect → infertility
🔑KEY POINTS TO REMEMBER- Corpus luteum secretes progesterone (secretory endometrium).
- Regresses in ~12 days if no pregnancy.
- Rescued by hCG if pregnancy occurs.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
The placenta is the fetomaternal organ providing nutrition, gas exchange, excretion, hormone secretion and protection for the fetus.
Functions
- Respiratory — O₂/CO₂ exchange
- Nutritive — glucose, amino acids
- Excretory — fetal wastes
- Endocrine — hCG, oestrogen, progesterone, hPL
- Barrier — partial (some drugs/germs cross)
The placenta transports substances and secretes pregnancy hormones. Function Example Respiratory O₂ / CO₂ Nutritive Glucose Endocrine hCG, progesterone Barrier Partial Applied
- Some drugs/infections cross (TORCH)
- Rh sensitisation across the placenta
🔑KEY POINTS TO REMEMBER- Placenta: respiratory, nutritive, excretory, endocrine, barrier.
- Makes hCG, oestrogen, progesterone, hPL.
- Only a partial barrier (TORCH, some drugs cross).
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).Definition
Menopause is the permanent cessation of menstruation (≥12 months amenorrhoea), usually at ~45–55 years, due to ovarian failure.
Mechanism
- Ovarian follicles exhausted
- ↓ Oestrogen and progesterone
- ↑ FSH and LH (loss of feedback)
Features
- Hot flushes, night sweats
- Mood changes, vaginal dryness
- Long-term: osteoporosis, ↑ cardiovascular risk
As follicles run out, oestrogen falls and gonadotropins rise, ending menstruation. Hormone Change Oestrogen ↓ FSH / LH ↑ Applied
- Hormone replacement therapy (HRT)
- Osteoporosis prevention
🔑KEY POINTS TO REMEMBER- Menopause = ovarian failure; ↓ oestrogen, ↑ FSH/LH.
- Features: hot flushes, dryness, osteoporosis.
- HRT for symptoms; watch bone health.
📚SOURCES: Guyton & Hall Textbook of Medical Physiology; Ganong’s Review of Medical Physiology; Textbook of Physiology (A.K. Jain).