The Endocrine System

blood

blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance.

• Homeostasis is the regulation of internal environment to maintain stable conditions around a set point.
• A hormone produces a slower, but longer lasting response.
• Nerves produce a quicker response with a shorter duration
• Negative feedback occurs when the effector response reduces the initial stimulus. This prevents wild fluctuation away from the set point. (ex: insulin and glucagon, antagonistic hormones)
• Positive Feedback amplifies the initial signal. (ex: oxytocin stimulates uterine contractions, which stimulate the release of more oxytocin)
• A Receptor detects a change away from the set point and then sends information to the control center (generally the hypothalamus or pituitary) by way of nerves of hormones. The Control Center compares the information to the set point and then sends an efferent signal to the effector, which then corrects the variable back toward the set point.

• Transfer of Heat in the blood: Dilating and constricting blood vessels (vasodilation/vasoconstriction) will control the flow of blood to various extremities. Heat is lost when blood flow is routed to the extremities and when it is confined to the core, heat is conserved. Warm arterial blood exhanges heat with cooler venous blood moving in the opposite direction. This is called countercurrent heat exchange.
• Thyroid: Hypothyroid-->low metabolism= Cold body temperature, Hyperthyroid--> high metabolic rate= overheating easily
• Hypothalamus: Cold thermoreceptors detect a drop in skin temperature and send nervous impulses to the hypothalamus. A heat promoting center monitros the fall in temperature and triggers responses that generate and conserve heat. Hot thermoreceptors detect a rise in skin temperature and send nervous impulses to the hypothalamus. The heat losing center monitors the rise in skin or core temperature and coordinates responses that increase heat loss. Hypothalamus sends efferent signals to the effectors.
• 3 mechanisms:
• 1. Sweat glands: the heat losing center signs signals to the sweat glands. Sweat is produced and evaporates. As the water evaporates, its cools off the body.
• 2. Skin arterioles: blood vessels dilate (more blood in skin to release heat) or constrict (less blood flow, so heat retained) to promote or prevent heat loss.
• 3) Muscles: Heat promoting center of the hypothalamus sends signals to muscles. This leads to the muscles rapidly contracting. The rapid contractions burn glucose, which releases heat into body tissues.
• The surrounding temperature forces the body to make corrections to keep its temperature relatively constant.
• An individual also seeks to control body temperature through different behaviors, such as seeking shade or removing clothing to counteract overheating, or may increase activity to counter cold.

• Glucose is the primary fuel for cellular respiration
• Glucagon promotes the increase of blood glucose by causing liver cells to break down or hydrolyze glycogen and release glucose to the blood
• Glycogen: a glucose polymer made by and stored in the liver
• Insulin: produced by the beta cells, and causes body cells to take up glucose from the blood, and liver cells take in glucose and convert it to glycogen.
• Both glucagon and insulin are protein hormones so they remain outside the cell and are water soluble.
• Glucagon and Insulin are antagonistic hormones.
• alpha and beta cells in the pancreatic islets, alpha cells produce glucagon and beta cells produce insulin.
• Pancreatic islets: small areas in the pancreas that contain alpha and beta cells.
• the Pancreas is also an exocrine gland, secreting fluids containing digestive enzymes into ducts.

• High glucose levels can be toxic but low glucose levels deprive cells of sufficient energy to carry out cellular respiration.
• Type I: Autoimmune disorder; insulin dependent/juvenile onset, immune system destroys beta cells of the pancreas so insulin can no longer be produced. It is treated by injections of insulin produced by genetically engineered bacteria.
• Type II: common in obese, sedentary, and middle-aged people because the body makes less insulin, or insulin resistance develops. It can often be managed by exercise and diet, and can be treated with insulin. 90% of people with diabetes have this form.
• A tendency toward diabetes can be hereditary.

target cells

• Steroids: testosterone, estrogen, progesterone, cortisol
• Tyrosine Derivatives: thyroxine
• Proteins: insulin, glucagon

• Steroids enter the cell directly because they are lipid soluble (non-polar). The receptor is internal, and is located in the cytoplasm. The steroid binds to the receptor. The hormone- receptor complex enter the nucleus and triggers the transcription of a gene. This causes production of a certain protein.
• Steroid--> Receptor (in cytoplasm) --> Hormone-receptor complex --> nucleus --> transcription of a gene
• Protein Hormones bind to receptors in the membrane. They can't enter the cell because they are polar, water soluble, and very large. This initiates a series of chemical reactions (signal transduction) that produces a second messenger inside of the cells which alters some cell function. This can include altering the transcription or expression of a gene or more often activation of an enzyme.
• Protein Hormone --> receptor on membrane --> Chemical reactions in cytoplasm --> second messenger --> change in cell function/or transcription

• The posterior is an extension of the hypothalamus. It grows downward toward the mouth during embryonic development. The posterior pituitary stores and secretes hormones (ADH and oxytocin(involved in milk release and labor contractions)) synthesized by neurosecretory cells of the hypothalamus. The axons of the neurosecretory cells connect the hypothalamus and posterior pituitary. They synthesize hormones and the posterior pituitary stores and then releases the hormones in response to a nervous impulse
• The anterior pituitary is connected to the hypothalamus by portal vessels. It synthesizes and secretes at least 6 different hormones, several of which target other endocrine glands. It is regulated by tropic hormones produced by neurosecretory cells in the hypothalamus. Some cause it to release hormones while others suppress the release of hormones. Tropic hormones (FSH, LH, TSH) travel through the portal vessels.

ADH, or antidiuretic hormone, acts on kidneys to promote water retention. It decreases urine output by increasing water reabsorption in the collecting duct. Osmoreceptors in the hypothalamus detect high solute concentration in the blood. Neurosecretory cells produce ADH, which is stored in the posterior pituitary. When osmoreceptors in the hypothalamus detect high solute concentration, ADH release from the posterior pituitary is triggered. When osmoreceptors detect normal blood solute levels, the production and secretion of ADH stop. This is negative feedback.

• Hormone: Oxytocin
• Chemical Class: Peptide
• Actions: stimulates contraction of uterus and mammary gland cells
• Regulated by: Nervous System
• Hormone: ADH
• Chemical Class: Peptide
• Actions: Promotes retention of water by kidneys
• Regulated by: Water/salt balance

• Hormone: Growth Hormone
• Chemical Class: Protein
• Actions: stimulates growth (especially bones) and metabolic functions
• Regulated by: Hypothalamic Hormones
• Hormone: Prolactin (PRL)
• CC: Protein
• Actions: Stimulates milk production and secretion
• Regulated by: Hypothalamic hormones
• Hormone: FSH
• CC: glycoprotein
• Action: stimulates production of ova and sperm
• Regulated by: Hypothalamic hormones
• Hormone: LH
• CC: glycoprotein
• Action: stimulates ovaries and testes
• Regulated by: hypothalamic hormones
• Hormone: TSH
• CC: Glycoprotein
• Action: Stimulates thyroid gland
• Regulated by: Thyroxine in blood, hypothalamic hormones
• Hormone: ACTH
• CC: Peptide
• Action: stimulates adrenal cortex to secrete glucocorticoids
• Regulated by: Glucocorticoids; hypothalamic hormones

• Hormone: T3 and T4
• CC: Amine
• Action: Stimulate and maintain metabolic processes
• Regulated by: TSH
• Hormone: Calcitonin
• CC: peptide
• Action: lowers blood calcium level
• Regulated by: Calcium in the blood

• Hormone: Parathyroid hormone (PTH)
• CC: peptide
• Action: Raises blood calcium level
• Regulated by: Calcium in blood

• Hormone: Insulin
• CC: Protein
• Action: Lowers blood glucose level
• Regulated by: Glucose in blood
• Hormone: Glucagon
• CC: Protein
• Action: Raises blood glucose level
• Regulated by: Glucose in blood

• Hormones: Epinephrine and Norepinephrine
• CC: Amine
• Action: Raise blood glucose level, increase metabolic activities, constrict certain blood vessels.
• Regulated by: Nervous System

• Hormone: Glucocorticoids
• CC: steroid
• Action: Raise blood glucose levels
• Regulated by: ACTH
• Hormone: Mineralocorticoids
• CC: steroid
• Action: promote reabsorption of Na+ and excretion of K+ in kidneys
• Regulated by: K+ in blood

• Hormone: Androgens
• CC: Steroid
• Action: Supports sperm formation, promote development and maintenance of male secondary sex characteristics
• Regulated by: FSH and LH

• Hormone: Estrogens
• CC: steroid
• Action: stimulate uterine lining growth, promote development and maintenance of female secondary sex characteristics
• Regulated by: FSH and LH
• Hormone: Progesterone
• CC: Steroid
• Action: Promotes uterine lining growth
• Regulated by: FSH and LH

• Hormone: Melatonin
• CC: Amine
• Action: Involved in biological rhythms.
• Regulated by: Light and dark cycles