IB Biology: UNIT 6.6 Hormones & Homeostasis

Thermoregulation

*Hot:* - Vasodilation: arterioles dilate so more blood enters skin capillaries and heat is lost - Sweating: Sudorific glands secrete sweat which removes heat when water changes state - Pilorelaxation: this means the hairs flatten - Stretching Out: by opening up, the body was a large surface area *Cold:* - Vasoconstriction: Arterioles get smaller to reduce blood going to the skin; keeping the core warm - Shivering: Rapid contraction and relaxing of skeletal muscles. Heat produced by respiration. - Piloerection: hairs on skin stand up - Curling up: making yourself smaller so smaller surface area

Female Reproductive System

*Ovary*- produces eggs and the hormone estrogen and progesterone *Oviduct*- Egg is released during ovulation, fertilization takes place here, embryo moves to the uterus *Uterus* - forms a thick lining and embryo is implanted on the thick wall *Cervix* - protects fetus during pregnancy and dilates during childbirth *Vagina* - receives semen and acts as a birth canal *Vulva* - protects internal part of female reproductive system

Male Reproductive System

*Testis* - produces sperm and testosterone *Scrotum* - holds testes outside the body and lowers body temperature *Epididymis* - stores sperm until ejaculation *Sperm duct* - transfers sperm during ejaculation *Seminal Vesicle* - produces fluid semen *Prostate Gland* - nourishes sperm with sugar to swim *Urethra* - transfers semen during ejaculation and urine during urination *Penis* - erects and penetrates into vagina for ejaculation during sexual intercourse

IVF (in vitro fertilization)

1. egg production is stimulated by hormone therapy (FSH, LH, and HCG) (make more eggs, 10-20) 2. eggs are retrieved from the ovary through a needle 3. sperm sample is provided to a lab dish 4. eggs and sperm combined to allow fertilization (then kept in incubators at 37 degrees C) 5. fertilized eggs are introduced into the uterus *Causes of Infertility:* *Women:* - ova not maturing or being released - abnormality in uterus that prevents implantation - antibodies in cervical mucus impair sperm *Men:* - unable to achieve an erection or ejaculation - low sperm count or sperm are abnormal with low motility - blocked vas deferens *Pros:* - allows infertile couples to have a child - embryonic stem cell therapy *Cons*: - expensive - risky and painful treatment - against natural selection

Thyroxin (Growth Hormone)

A hormone released by the thyroid gland to regulate the metabolic rate and controls body temperature 1. A stimulus causes the hypothalamus to secrete TRH, which acts as on the pituitary gland 2. Thyroptic cells in the pituitary are stimulated to release thyroid-stimulating hormone (TSH) 3. TSH acts on cells of the thyroid gland. Follicular cells are stimulated to release thyroid hormone (TH) 4. TH stimulates target cells to increase metabolic activities, resulting in an increase in basal body temperature 5. Increased TH levels cause heat production in target cells; that increase in temperature is detected by the hypothalamus as it monitors blood temperature and inhibits the secretion of TRH by the hypothalamus. TH also blocks the interactions of TRH from the hypothalamus and pituitary gland to prevent the formation of TSH *Possible Question:* Explain the hormone that controls metabolic activity on body temperature (6)

Diabetes

An auto-immune disorder where a person glucose level is constantly high. This results in the presence of glucose in urine and damages in tissues, nerves which affects the reabsorption of water in kidneys Results: - increase urine volume, frequent urinating - Thirsty, tired, weight loss Two types of diabetes: *Type 1:* Early onset (childhood) of diabetes, a condition in which the body fails to produce insulin and results in insulin deficiency. Requires the person to inject insulin. Less or no insulin binds to a receptor, glucose stays outside the target cell. *Type 2*: Late onset (adulthood) of diabetes. Can be controlled by diet and/or medication. The pancreas produces enough insulin but something goes wrong either with receptor binding or insulin signalings in the target cell, glucose stays out the cell in the blood.

Blood Sugar Control

Blood sugar is controlled by two hormones: - insulin & glucagon (polypeptides) - they are secreted by beta and alpha cells in the pancreas *Alpha cells* produce *glucagon*. If the blood sugar gets too *low*, it stimulates the liver to convert *glycogen into glucose* and release it into the blood, so the blood sugar *increases* *Beta cells* produce *insulin*. If the blood sugar level is *high*, it stimulates the liver and the skeletal muscle converts *glucose into glycogen*, so the blood sugar *decreases.* Insulin secretes within a minute after a meal and will continue for several hours after a meal and will be broken down by the liver.

Possible Questions

Explain/outline negative feedback of glucose concentration State the hormones that are produced in the pancreas (beta cells produce insulin, alpha cells produce glucagon) State the role of insulin (or) glucagon - insulin decreases glucose concentration. The liver converts glucose into glycogen. Stored as polypeptide Distinguish Type I vs Type II Diabetes / Causes of Diabetes

Explain the role of hormones in the regulation of the mentstrual cycle (8 marks)

FSH and LH are produced by the pituitary gland, & estrogen and progesterone are produced by the ovary FSH stimulates the ovary to promote the development of a follicle The developing follicles secrete estrogen, which inhibits FSH (negative feedback) Estrogen stimulates the growth of endometrium and stimulates LH secretion (positive feedback) LH stimulates follicle growth and triggers ovulation, the follicle becomes corpus luteum The corpus luteum secretes estrogen and progesterone, which maintain the endometrium, & inhibits FSH and LH After two weeks, the corpus luteum degenerates as progesterone and estrogen levels fall, this triggers menstrual bleeding, the loss of endometrium The pituitary gland secretes FSH and LH, as they are no longer inhibited and the menstrual cycle continues

Sex Determination

Fusion of male gamete with a female gamete results in zygote information in human reproduction. Initially, the development of the embryo is the same, and the embroynic gonads develop into either testes or ovary by the presence and absence of SRY gene If the SRY gene is present, the embryonic gonads develop into testes. The gene is located in the *Y* chromosome. SRY codes for DNA binding protein TDF (testes development factor) TDF stimulates the expression of other genes that cause testis development, testosterone can be produced. In absence of TDF protein and SRY gene, ovaries will be developed.

Estrogen and Progesterone

If the SRY gene is absent, the embryonic gonads develop as ovaries and female hormones estrogen and progesterone is always present and is first produced by mother ovaries and later by the placenta. The absence of testosterone and the presence of maternal estrogen and progesterone results in female organ development. During puberty, the level of secretion of estrogen and progesterone increase cause of the development of secondary female sexual characteristics such as breast enlargement, pubic hair growth, armpit hair growth, widening pelvis, the menstrual cycle starts.

The Endocrine System

Key Endocrine Glands: - pineal gland - pituitary gland - thyroid gland - thymus - adrenal gland - pancreas A stimulus is received and processed. Hormones are secreted directly into the blood They are carried to the target tissues. The action of the hormone changes the condition of the tissue. This change is monitored through feedback. Most hormonal change results in negative feedback.

Homeostasis

Maintaining a constant internal environment Maintains optimal conditions for enzyme action and all cell functions In the human body, homeostasis includes control of: - blood glucose concentration - body temperature - water levels

Explain the control of blood glucose (8 marks)

Pancreatic cells monitor blood glucose; Absorption of glucose from digestion in the intestine increase blood sugar/fasting reduces blood sugar ex. Glucoregulation is an example of negative feedback which uses insulin and glucagon If blood glucose is *too high*, beta cells of the pancreas produce insulin. Insulin stimulates uptake of glucose to cells, for example, muscles. Insulin stimulates liver/fat cells to store glucose as glycogen, leading to a decrease in blood glucose If blood glucose is *too low*, the alpha cells of the pancreas produce glucagon. It stimulates the liver to break glycogen into glucose, which leads to increased blood sugar.

Hormones

The chemicals produced by the *endocrine gland*, taken into the blood stream and given to target cells and destroyed in *liver* ex. insulin, thyroxin, adrenaline, estrogen/progesterone, testosterone Insulin and Thyroxin are *globular proteins* Estrogen, Progesterone, and Testosterone are *steroids* (fat hormones) Hormones are slower than nerve impulses (chemical signal and nerve impulses are electrical)

Menstrual Cycle

The cycle is controlled by 4 hormones: *FSH* - stimulates follicle development *LH* - matures follicle, causes ovulation *Estrogen* - *Progesterone* - *HCG* - keeps estrogen and progesterone high *Oxytocin* - causes uterus contraction *Follicular Phase:* Follicles develop in the ovary, and in each follicle, an egg is stimulated to grow. The uterus endometrium lining thickens, the mature follicle breaks, and egg is released into oviduct and the other follicles degenerate. *Luteal Phase*: After releasing the egg, corpus luteum and continues the uterus endometrium lining and produce the hormone progesterone. If fertilization does not take places, the corpus luteum break, and the uterus lining breaks. *Menstrual Phase*: Shedding of endometrium lining takes place and menstrual cycle begins

Leptin

The hormone produced by cells in adipose tissue and acts on the hypothalamus to inhibit appetite. The concentration of leptin in the blood is controlled by food intake and the amount of adipose tissue in the body. Leptin binds to receptor membrane of the cells. If adipose tissue increases, leptin concentration in blood increase causing long-term appetite inhibition and reduced food intake. *Possible questions:* Explain the action of leptin (3) - Leptin is a protein hormone produced in adipose tissue. It activates the hypothalamus which decreases hunger and food intake. The people who have a defect in leptin receptors become obese. People with ob/ob recessive allele cannot produce leptin. (pg. 332)

Melatonin

The hormone produced by the pineal gland controls circadian rhythm. Controlled by the hypothalamus and SCN (suprachiasmatic nuclei) The effect of melatonin is the sleep-wake cycle. High level of melatonin results in drowsiness and promotes sleep in the night. Low levels of melatonin results in waking up. Melatonin receptors are found in the kidney. Circadian rhythms are physical, mental and behavioral changes that respond primarily to light and darkness in the environment. These roughly 24-hour cycles of changes are found in most organisms, from humans to fruit flies, plants and even tiny microbes. Circadian rhythms determine sleep patterns, contribute to jet lag and the groggy feeling you may experience after daylight savings time. Circadian rhythms also influence hormone production, hunger, cell regeneration, and body temperature and are associated with obesity, depression and seasonal affective disorder. *Possible Questions:* Explain the action of melatonin (4): - Melatonin hormone is secreted by the pineal gland which controls SCN and hypothalamus. Melatonin levels alter the sleep/wake pattern. The abiotic factor that controls melatonin is a light/dark environment. In dark, the melatonin levels increases and lead to sleep.

Testosterone

The steroid hormone causes the development of male genitalia and also the development of male secondary characteristics and gamete (sperm) At puberty, testosterone secretion increase and stimulates sperm production in the testes (primary characteristics), and also cause secondary characteristics such as growth of pubic hair, widening shoulders, deepening voice, etc. (due to growth of the larynx)

Hypothyroidism

Thyroxin hormone is given to all body cells and it contains 3 iodine atoms in its structure. Prolonged deficiency of iodine in the diet prevents Thyroxin synthesis and leads to hypothyroidism. *Effects:* - Lack of energy - Depression and forgetfulness - Weight gain and loss of appetite, less glucose and fat are broken down - Less heat is produced - Constipation - Impaired brain development in children