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York University
Natural Science
NATS 1675
Barbara Czaban

LECTURE 19 – FETAL PERIOD OF DEVELOPMENT FETAL PERIOD (WEEK 9 – BIRTH) - continued differentiation & growth of tissues & organs - Increase in crown – rump length & weight - called the ‘fetus’ - At end of week 8 – 3 cm long & bones began to calcify, skeletal muscles exhibit spontaneous contradictions th - Since 4 week heart beats & blood circulates - Heart & liver large forms prominent ventral bulge - Head nearly half body Amnion bubble surrounding fetus – umbilical cord is attached to the chorion. FETAL PERIOD – rdriod of growth, no form change but increase in size (esp. inner organs) and greatest weight incrSTse occurs at 3 trimester. - 1 growth influenced by maternal hormones (passing through placenta) and later fetal hormones influence growth MONTHS 3&4 – head slows in growth & hair develops, cartilage replaced by bone, distinguish sex, can hear heartbeat, ~6 inches/~6 ounces. MONTHS 5-7 – fetal movement felt, fetal position, eyelids open, ~12 inches/~3 pounds. MONTHS 8&9 – per week weight gained, fetus rotates (head toward cervix), ~7.5 pounds/~20.5 inches. FETAL CIRCULATION & THE PLACENTA PLACENTA FUNCTION 1. SOURCE OF PREGNANCY HORMONES – PROGESTERONE & ESTROGEN - prevents new follicles from maturing, maintain endometrium 2. PLACENTAL EXCHANGES GASES, NUTRIENTS, WASTES, MAINTAINS TEMP. ETC. PLACENTAL CIRCULATION brings maternal & fetal circulations into a close relationship EMBRYONIC BLOOD (OXYGEN POOR) flows inVILLUS VESSEL (separated from maternal blood) - Umbilical arteries brings oxygen-poor blood from fetus to placenta (away from fetus heart) - Umbilical veins brings oxygen-rich blood from placenta to fetus (toward fetus heart) - Fetal capillaries pick up oxygen MATERNAL BLOOD (OXYGEN RICH) enters INTERVILLUS SPACE - Spiral arteries open into space, moves blood away from maternal heart - Uterine veins carry oxygen-poor blood toward mother’s circulatory system & heart PLACENTAL BARRIER – composed of structures that separate maternal & fetal blood PLACENTAL EXCHNAGE occurs via classic membrane transport mechanisms (pg. 54-57) PASSIVE TRANSPORT (without energy consumption) 1)Simple diffusion: Gases, non-polar molecules & fat soluble substances diffuse from the side with higher concentration to lower concentration 2)Osmosis: movement of water across selective-permeable membrane, water enters placenta via specialized pores, larger volumes of water cross placenta through aqua porins (water channels) 3)Simplified Transport (Passive facilitated diffusion): Glucose, amino acids & other larger molecules cross placenta with help of facilitated transporter molecules (from are of high to low concentration) ACTIVE TRANSPORT (energy requiring – usually ATP) - Movement of ions across membrane from side with lower concentration to side with higher concentration with help of active transport molecule UMBILICAL ARTERIES away from fetus heart UMBILICAL VEINS toward fetus heart MATERNAL BLOOD IN LACUNA (CAVITY) - Diffusion into fetal capillaries – oxygen and nutrients into fetal blood - Diffusion waste substances into maternal blood NOTE: Fetal & maternal blood does not mix because exchange of material b/w two occurs achorionic villi. There is aplacental barrier (tissue). UMBILICAL PLACENTAL CIRCUIT -INTERNAL ILIAC ARTERIES give rise to twumbilical arteries - low in oxygen & high is 2O & wastes; umbilical arterial bdischarges waste in placenta -UMBILICAL VEIN(ONE) oxygen & nutrient loaded returned to fetus - Some venous blood is nourished through liver - Most venous blood bypass liver via a shunshunt venosus’. - leads tinferior vena cava (in heart) FETAL LUNGS NOT FUNCTIONAL YET - Lungs receive only trickle of blood; sufficient to meet metabolic need during development FETAL CIRCULATORY PATTERNS CHANGE AT BIRTH - Neonate cut off from placenta; lungs expand with air & permits blood flow & gas exchange through lungs CHROSOMAL SEX DETERMINATION Our cells contain 23 pairs of chromosomes - 22 pairs oautosomes ; 1 pair sex chromosome (XY males; XX females) - Males produce half Y carrying sperm, and half X carrying sperm - All eggs carry the X chromosome Sex of child determined by type of sperm that fertilizes egg - X carrying sperm fertilizes egg – FEMALE - Y carrying sperm fertilizes egg – MALE PRE-NATAL HORMONES AND SEX DIFFERENTIATION Gonads (testes, ovaries) develop at 5/6 weeks as gonadal ridges Two sets of ducts adjacent to each gonadal ridge - Mesonephric ducts (Wolffian ducts) develop into male reproductive system - Paramesonephric ducts (Mullerian ducts) develop into female reproductive tract SRY GENE (sex determining region of Y chromosome) - Males codes for protein, testes determining factor (TDF) initiates development of testes - Secretes testosterone 7-9 weeks - Mesonephric ducts develop into male anatomy - Testes secrete mullerian-inhibiting factor causes degeneration of paramesonephric ducts MALE (7-8 Weeks) FEMALE (8-9 WEEKS) - Testes -Ovaries - Paramesonephric duct degenerating - Paramesonepric duct forms uterine tube - Mesonephric duct form ductus deferens - Mesonephric duct degenerating - Seminal vesicle - Fused paramesonephric ducts form uterus - Urogenital sinus forms the urethra - Urogenital sinus forms the urethra & lower vagina DEVELOPMENT OF EXTERNAL GENITALIA Similarity of external genitalia becomes of both sexes: Genital tubercle becomes head (glans) of penis OR glans clitoris Pair of urogenital folds encloses male urethra of forming penis OR forms labia minora Pair of labioscrotal folds becomes scrotum OR labia majora By week 12, females & male genitalia are distinctly formed - Organs that develop from the same embryonic structure arehomologous structures - Penis is homologous to clitoris; scrotum is homologous to labia majora LECTURE 21 – HORMONES, REPRODUCTION & DEVELOPMENT Hormones: chemically active compounds produced in one area of body but have effect elsewhere Signaling Molecules: coordinates & manages activity of body cells; responsible for sequential changes of growth, development & maturation; involved in homeostasis - Secreted by endocrine glands, endocrine cell, neurons – enter body stream, arrive at target cells - Hormone action dependent on target cell – one hormone can have many target cells. A hormone can have varying effects on different tissues. Testosterone – a masculinizing hormone OH – O Estradiol – a feminizing hormone OH – HO THERE ARE 2 MAIN CLASSES OF HORMONE Steroid hormone: includes testosterone & estrogen; Lipid-soluble so can pass through phospholipid bilayer of cell membrane Non-steroid hormone: example peptide hormones; Not lipid-soluble so cannot penetrate the cell membrane ALL HORMONES BIND TO PROTEIN RECEPTORS - Signal received – signal converted – cells respond - Different types of hormones cause changes in target cells by different mechanisms STEROID HORMONES – MECHANISMS - lipid-soluble (diffuse through target cell’s plasma membrane) - Moves into nucleus & binds to a receptor - Hormone-receptor complex triggers gene activity in the DNA - Genes in DNA contain info for making proteins (gene product) - Gene – mRNA – protein - Resulting protein carries out cell’s response to hormone signal EXAMPLE 1. Steroid hormone molecule moved from blood into interstitial fluid bathing a target cell 2. Lipid soluble, so steroid hormone diffuses across target cell’s plasma membrane 3. Hormone diffuses through cytoplasm & nuclear envelope – binds with its receptor in the nucleus 4. Hormone receptor complex triggers transcription of a specific gene 5. Resulting mRNA moves into cytoplasm & translated into protein (gene product) NON-STEROID HORMONES – MECHANISMS - water-soluble (don’t enter target cell; binds to cell’s membrane protein receptor) - Act indirectly, by second messengers (cyclic AMP) - Cyclic AMP signals cell to activate another enzyme etc. until final response achieved -The activation/inhibition of proteins in cytoplasm) - More than one response may be initiated, depending on hormone & specific system it affects EXAMPLE 1. Non-steroid hormone diffuses from blood into interstitial fluid bathing the plasma membrane of a cell 2. Hormone binds with receptor. Binding activates an enzyme that catalyzes the formation of cyclic AMP from ATP inside cell. 3. Cyclic AMP activates another enzyme inside the cell. 4. Enzyme activated by cyclic AMP activates another enzyme, may lead to a specific response. 5. Enzyme activated by cyclic AMP also may cause a different response. STEROID 1. Lipid soluble hormone diffuses into cell; binds to receptor in cytoplasm/nucleoplasm 2. Activated – receptor – complex initiates gene transcription 3. Messenger RNA initiated by hormone leaves nucleus & directs formation of new protein 4. Cell uses new proteins to alter activity of cell NON-STEROID 1. water soluble hormone (first messenger) binds to a specific receptor & activates attached enzymes in cell 2. Activation of adenylate cyclase causes formation of cAMP 3. cAMP serves as second messenger to activate protein kinases 4. Activated protein kinases phosphorylate cellular proteins 5. Phosphorylated proteins cause reactions that produce psychological responses. ENDOCRINE SYSTEM Endocrine glands secrete hormones into bloodstream - Usually gets released in short bursts -Gland stimulated by signal from nervous system/another endocrine gland (hormone released to blood) -When stimulation stops, hormone concentration in blood drops Hypothalamus – regulates the pituitary Pineal Gland – helps with sleep & puberty (melatonin) Pituitary Gland – stimulates the thyroid (TSH), adrenal glands (ACTH), water retention (ADH), uterine contraction (oxytocin), egg/sperm development (FSH, LH), milk production hormone (prolactin), growth hormone (GH) Thyroid Gland – increases metabolic rate (T3&T4), regulates development, lowers blood calcium (calcitonin) Thymus – produces T cells (thymosine) Ov ary – stimulates secondary sex characteristics (estrogen & progesterone) Testes – stimulates secondary sex characteristics (testosterone) Pancreas – monitors blood glucose (insulin & glucagon) Parathyroid Glands – raises blood calcium (PTH) Adrenal Glands – raises blood glucose (cortisol, epinephrine, norepinephrin), affects sodium/potassium levels (aldosterone), produces small amount of sex hormones Endocrine hormones direct sequential growth maturation. - Directs growth of bones, muscles, nervous tissue. Maintains healthy metabolic rate, monitor sleep patterns, maintain ion & water, regulate blood levels of calcium & glucose. Stimulate appearance of secondary sexual characteristics & production of eggs/sperm. Final growth spurt occurs at age 12-17 human growth hormone surges through body - Rapid increase in size muscular & skeletal systems. Internal organs grow: lungs, stomach, kidneys double in size, brain increase 5% During puberty reproductive organs begin to function. - Directed by production gonadotropin releasing hormone (GnRH) from hypothalamus - GnRH causes release oFSH, LH byanterior pituitary gland - Females: ovaries respond bmaturing egg follicles , produceestrogen -Males: produce sperm & testosterone due to FSH, LH Puberty – onset of menstrual cycle in females (menarche), appearance of nocturnal emission in males. ENDOCRINE GLANDS that are important to sex & reproduction 1) HYPOTHALAMUS & PITUITARY 2) ADRENAL GLAND (ADRENAL CORTEX) 3) GONADS 1) HYPOTHALAMUS & PITUITARY HYPOTHALAMUS integrates endocrine & nervous function. - Neurosectory cells of hypothalamus produce hormones. These hormones stored/regulate activity of pituitary gland (to produce other hormones) PITUITARY GLAND obeys hormonal order from hypothalamus - Located at base of hypothalamus; 2 discrete part with very different functions 1) Posterior pituitary 2) Anterior pituitary POSTERIOR (NERVOUS TISSUE) -Secretes Antidiruetic hormone (ADH) and oxytocin (OT) - ADH in kidneys cause water conservation; OT in mammary glands cause milk to move and in uterus causes uterine contractions during childbirth ANTERIOR (GLANDULAR, TISSUE) -Secretes ACTH in adrenal glands releasing cortisol (adrenal steroid hormone) -Secretes TSH in thyroid gland releasing thyroid hormones -Secretes FSH in ovaries & testes releasing estrogen, egg maturation/sperm formation -Secretes LH in ovaries & testes releasing progesterone, ovulation, corpus luteum/ testosterone & sperm release - Secretes PRL in mammary glands milk production -Secretes GH in most cells promotes growth, protein synthesis, cell division etc. POSTERIOR (NERVOUS TISSUE) A) Secretory neurons in hypothalamus synthesize ADH & OT B) ADH & OT move downward inside axons of secretory neurons & accumulates (are stored) in axon ending C) Action potentials triggers release of stored hormones & enters blood capillaries in posterior lobe of
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