Week 1

hypothalamus and pituitary glands (endocrine glands) are of major importance since they act as the coordinating centres of the endocrine system

Responsible for maintaining the body’s internal balance (homeostasis) by stimulating or inhibiting major bodily functions such as • the heart rate and blood pressure, body temperature, fluid and electrolyte balance The hypothalamus is also considered the master regulator of the endocrine system. • Regulatory hormones secreted by the hypothalamus are transported by the hypophyseal-portal system to the anterior and posterior pituitary, prompting the release of secondary hormones that can affect various organ functions

The hypothalamic hormones are referred to as releasing hormones and inhibiting hormones, reflecting their influence on pituitary hormones

Functions via three mechanisms • Secretes regulatory hormones • Secretes releasing hormones (RH) • Secretes inhibiting hormones (IH) Acts as an endocrine organ • Releases antidiuretic hormone and oxytocin to the pituitary gland Contains autonomic nervous system centres • Exerts control over the suprarenal medulla

the hypothalamus is responsible for creating or controlling hormones

• A pea-sized gland that is housed within a bony structure (sella turcica) at the base of the brain. • The sella turcica protects the pituitary but allows very little room for expansion. • Attached to the hypothalamus via the infundibulum Consists of two lobes • Adenohypophysis: anterior lobe releases nine peptide hormones • Neurohypophysis: posterior lobe releases two peptide hormones

• Controls the function of most other endocrine glands and is therefore sometimes called the other master gland. • In turn, the pituitary is controlled in large part by the hypothalamus, a region of the brain that lies just above the pituitary. • By detecting the levels of hormones produced by glands under the pituitary’s control (target glands), the hypothalamus or the pituitary can determine how much stimulation the target glands need.

The anterior pituitary (or adenohypophysis) is a lobe of the gland that regulates several physiological processes (including stress, growth, reproduction, and lactation). Endocrine cells of the anterior pituitary are controlled by regulatory hormones released by parvocellular neurosecretory cells in the hypothalamus. Divided into anatomical regions known as the pars tuberalis, pars intermedia, and pars distalis.

Produces seven hormones. • Growth hormone (GH) • Thyroid-stimulating hormone (TSH) • Adrenocorticotropic hormone (ACTH) • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH) • Beta endorphin • Prolactin Of the hormones of the anterior pituitary, TSH, ACTH, FSH, and LH are collectively referred to as tropic hormones (trope- = “turning”) because they turn on or off the function of other endocrine glands.

The posterior pituitary does not produce any hormones of its own, rather, it stores and secretes two hormones made in the hypothalamus: • Oxytocin causes the uterus to contract during childbirth and immediately after delivery to prevent excessive bleeding. • Vasopressin (also called antidiuretic hormone) regulates the amount of water excreted by the kidneys and is therefore important in maintaining water balance in the body.

Pituitary disorders can cause a range of symptoms. • Challenging to diagnose. They share these traits: • The pituitary gland may raise or lower one or more hormones. • A hormone imbalance can cause physical or mood changes. • At the same time, pituitary disorders often develop slowly. • It may take a long time until you notice symptoms. Symptoms of pituitary disorders are like those of other diseases. • Many people are misdiagnosed or go undiagnosed

Disorders that result from overproduction of pituitary hormones include • Acromegaly or gigantism: Growth hormone • Cushing disease: Adrenocorticotropic hormone ( ACTH), • Galactorrhea (the secretion of breast milk by men or by women when not pregnant): Prolactin • Erectile dysfunction: Prolactin • Infertility (particularly in women): Prolactin

• Disorders that result from under production of pituitary hormones include • Central diabetes insipidus: Vasopressin • Hypopituitarism: Multiple hormones

The nervous system and the endocrine system work together to monitor the body’s activities • The nervous system produces short-term, very specific responses • The endocrine system: many times it produces long-term, general responses Endocrine system is composed of glands that secrete chemicals called hormones into the bloodstream for the control of body functions. The role of the endocrine system is to maintain the body in balance through the release of hormones (chemical signals) directly into the bloodstream. • Hormones transfer information and instructions from one set of cells to another. • Many different hormones move through the bloodstream, but each type of hormone is designed to affect only certain cells.

Hormones are chemical substances that affect the activity of another part of the body (target site). • Hormones serve as messengers, controlling and coordinating activities throughout the body. • Upon reaching a target site, a hormone binds to a receptor, much like a key fits into a lock. • Once the hormone locks into its receptor, it transmits a message that causes the target site to take a specific action. • Hormone receptors may be within the nucleus or on the surface of the cell

• Pituitary gland • Hypothalamus • Thyroid gland • Thymus gland • Suprarenal glands • Pineal gland • Parathyroid glands • Pancreas • Reproductive glands

Functional • Endocrine Hormones – Travel through the blood to act at a site distant from the secreting cell or gland • Paracrine Hormones – Act on cells near the secreting cell • Autocrine Hormones – Act on the secreting cell • Neurocrine Hormones – Secreted by neural cells • neurotransmitters • neurohormones Chemical • Protein & Polypeptide • Amine (amino acid derived) • Steroid

Non-tropic hormones are hormones that directly stimulate target cells to induce effects. • For example, aldosterone acts directly on the kidney to promote reabsorption of sodium, which causes an increase in blood pressure Tropic hormones, which act on other endocrine glands to stimulate (or inhibit) release of a second hormone. • For example, thyroid-stimulating hormone is responsible for stimulating the release for thyroid hormone by acting on the thyroid gland

• Signal Chemicals • Made in endocrine cells • Transported via blood • Receptors on target cells

Neurotransmitters are chemicals secreted by neurons that diffuse across a small gap to the target cell. neurons use electrical signals as well. Neurohormones are chemicals released by neurons into the blood for action at distant targets

• Local communication • Signal chemicals diffuse to target Example: Cytokines • Autocrine–receptor on same cell • Paracrine–neighboring cells

• Grouped according to chemical structure. • Steroid hormones are fat-soluble molecules made from cholesterol. Non- steroidal • Protein and Amino acid derivatives, such as epinephrine, are water-soluble molecules derived from amino acids (the building blocks of protein).

Most water-soluble hormones • Like the amino acid derivatives and peptides, can travel freely in the blood because they “like” water. • However, they are repelled by lipid or fatty structures such as the membranes that surround the cell and nucleus. • Because of this, these hormones generally bind to receptor sites on the outside of the cell and signal from there. Fat-soluble hormones • Like the sex hormone steroids estrogens and androgens, are fat soluble and water repellent. • That is, they “like” lipid or fatty structures such as those surrounding cells but are generally repelled by watery areas. • Steroids generally travel to their target cells attached to a special carrier protein that “likes” water (such as, sex steroid hormone binding globulin and serum albumin). • The hormones detach before passing into the cell where they bind to receptors.

• Products of translation • Regulated secretion: The cell stores hormone in secretory granules and releases them in “bursts” when stimulated. This is the most commonly used pathway and allows cells to secrete a large amount of hormone over a short period of time. • Constitutive secretion: The cell does not store hormone but secretes it from secretory vesicles as it is synthesized.