Endocrine System

Glands and HormonesThe Endocrine System consists of glands and

tissues that secrete hormones

Endocrine Glands: ductless; secrete hormones directly into tissue fluid

Hormones: chemical signals that affect the behavior of other glands or tissues; each type has unique composition◦Influence metabolism of cells, growth and

development of body parts, and homeostasis

Categorize Hormones 2 classifications:

◦ Peptide Hormones (proteins, glycoprotein, modified amino acids)

◦ Steroid Hormones (lipids, estrogen, progesterone, testosterone)

Peptides: stay outside cell and directs activities within

◦ Bind to receptor protein in plasma membrane and activate “second messenger”

◦ Common second messengers found in many body cells include cyclic AMP (cAMP, made from ATP) and calcium

Steroids: have same four-carbon ring complex, but each has different side chains

◦ Diffuse across plasma membrane and other cellular membranes

◦ Bind to receptor proteins once inside cell

Hormone Release

Insulin release is controlled by negative feedback, hormonal control, and neural control

Release of hormones is controlled by different mechanisms:

1. Negative feedback controls hormone release

2. Hormone release controlled by actions of others

3. Hormone release controlled by nervous system Release is usually controlled by a negative feedback system for the

majority of hormones Negative Feedback System: stimulus causes body response Hormone release can also be controlled by certain

stimulating/inhibiting hormones Few instances where positive feedback controls release of hormones

Nervous SystemThe Nervous System plays a

role in the Endocrine System; they work together to regulate the organs of the body

The Nervous System is an important controller of the Endocrine System

The brain can make appropriate adjustments to hormone secretion which ensures homeostasis; the endocrine system is involved in homeostasis

Hypothalamus & Pituitary GlandHypothalamus: regulates internal environment◦Through autonomic system, helps control

heartbeat/body temperature/water balance◦Also controls glandular secretions of pituitary

gland (hypophysis)

Pituitary Gland: attached to base of brain that consists of anterior and posterior lobes◦Posterior Pituitary (Neurohypophysis)◦Anterior Pituitary (Adrenohypophysis)

HypothalamusOxytocin: other hormone made in hypothalamus,

causes uterine contraction during childbirth and milk letdown when baby is nursing

Hypothalamic-releasing Hormones: one of many hormones produced by the hypothalamus that stimulates secretion of anterior pituitary hormone

Hypothalamic-inhibiting Hormones: one of many hormones produced by the hypothalamus that inhibits secretion of anterior pituitary hormone

Pituitary GlandPosterior Pituitary: a portion of the pituitary gland

connected by a stalk to the hypothalamus

Diabetes Insipidus: person produces copious amount of urine with a resultant loss of ions from blood

Deals with Posterior Pituitary

Antidiuretic Hormone (ADH): hormone released from pituitary lobe of pituitary gland that enhances water conservation by kidneys with Posterior Pituitary

Sometimes called Vasopressin

Thyroid and Parathyroid GlandsThyroid Gland: large gland located in the neck,

where it is attached to trachea just below larynx Composed of a large number of follicles, each

small spherical structure made of thyroid cells filled with triiodothyronine and thyroxine

Thyroid-Stimulating Hormone (TSH): hormone that causes thyroid to produce thyroxine

Parathyroid Gland: embedded in the posterior surface of the thyroid gland

Thyroid Gland Myxedema: occurrence of hypothyroidism in adults; characterized by

lethargy, weight gain, loss of hair, slower pulse rate, lowered body temperature, and thickness and puffiness of the skin

Hyperthyroidism: (oversecretion of thyroid hormone), thyroid gland is overactive, and a goiter forms (exophthalmic goiter), also be caused by thyroid tumor

Congenital Hypothyroidism: when thyroid fails to develop properly, individuals with this condition are short and stocky and have had extreme hypothyroidism (undersecretion of thyroid hormone)◦ Therapy can initiate growth, but unless treatment is begun within the first two

months of life, mental retardation results Thyroid hormones:

◦ increase the metabolic rate

◦ do not have a single target organ

◦ stimulate all cells of the body to metabolize at a faster rate

◦ more glucose is broken down, and more energy is utilized

Parathyroid GlandParathyroid Hormone (PTH): causes the blood phosphate

level to decrease and the ionic blood calcium level to increase

Calcitonin: a hormone secreted by the thyroid gland when the blood calcium level rises, from the thyroid gland and the parathyroid gland and hormones, maintain the blood calcium level within the normal limits

Hypocalcemic Tetany: when insufficient parathyroid hormone production leads to a dramatic drop in the blood calcium level◦ In tetany, the body shakes from continuous muscle

contraction. This effect is brought about by increased excitability of the nerves, which nerve impulses spontaneously and without rest. In severe cases, it is fatal.

Adrenal Gland Adrenal Gland: sits atop the kidneys

Adrenal Medulla: inner portion of gland, under nervous control, hypothalamus initiates nerve impulses that travel by way of the brain stem, spinal cord, and sympathetic nerve fibers to the adrenal medulla, which then secretes its hormones

Adrenal Cortex: outer portion of gland, under control of ACTH

Adrenocorticotropic Hormone (ACTH): stimulates adrenal cortex to produce its hormones

These portions have no physiological connection with one another Stress of all types, including emotional and physical trauma, prompts the

hypothalamus to stimulate the adrenal glands

Epinepghrine (Adrenaline) and Nonrepinephrine (Nonadrenaline): produced by the adrenal medulla and rapidly bring about all the body changes that occur when an individual reacts to an emergency situation◦ The release of epinephrine and nonrepinephrine achieves the same results as

sympathetic stimulation – the "fight-or-flight" responses: increased the heart rate, rapid respiration, dilation of the pupils, etc.

Adrenal Cortex Adrenal Cortex Hormones:

◦ provide a long-term response to stress◦ secretes small amounts of both male and female sex hormones◦ promote skeletal growth in adolescents◦ male hormones from the adrenal gland stimulate the growth of axillary and

pubic hair at puberty◦ help sustain sex drive, or libido, in both men and women

2 major types: ◦ Mineralocorticoids ◦ Glucocorticoids

Mineralocorticoids: regulate salt and water balance, leading to increases in blood volume and blood pressure◦ Aldosterone is the most important◦ It also primarily targets the kidney where it promotes renal absorption of

sodium and water, and renal excretion of potassium◦ Secretion of mineralocorticoids from the adrenal cortex is influenced by

ACTH (adrenocorticotrpic hormone of corticotropin) from the pituitary gland

Adrenal Cortex Cont.

Glucocorticoids: regulate carbohydrate, protein, and fat metabolism, leading to an increase in blood glucose level

Cortisol: produced by the adrenal cortex, counteracts inflammatory response that leads to pain and swelling of joints in arthritis and bursitis

Cortisone: medication often administered for inflammation of joints, and other glucocorticoids can relieve swelling and pain from inflammation

Addison Disease: level of adrenal cortex hormone is low due to hyposecretion

Cushing's Syndrome: level of adrenal cortex hormone is high due to hypersecretion

Pancreas Pancreas: long organ that lies transversely in the abdomen between the kidneys and

near the duodenum of the small intestine Composed of two types of tissue:

◦ Exocrine◦ Endocrine

Endocrine Tissue: pancreatic islets, produces and secretes the hormones insulin and glucagon directly into the blood

Exocrine Tissue: produces and secretes digestive juices that go by way of ducts to the small intestine

Insulin and Glucagon: antagonistic hormones, both produced by the pancreas, help maintain the normal level of glucose in the blood

Insulin: secreted when the blood glucose level is high, stimulates the uptake of glucose by most body cells, not necessary for the transport of glucose into brain or red blood cells, but muscle cells and adipose tissue cells require insulin for glucose transport

Glucagon: secreted from the pancreas, when the blood glucose level is low; the major target tissues of glucagon are the liver and adipose tissue, stimulates the liver to break down glycogen to glucose and to use fat and protein in preference to glucose as energy sources

Pancreas Cont. Diabetes Mellitus: fairly common hormonal disease in which insulin-sensitive

body cells are unable to take up and/or metabolize glucose

Hyperglycemia: the blood glucose level is elevated; symptoms include perspiration, pale skin, shallow breathing, and anxiety

Polyphagia: person becomes extremely hungry

Insulin-dependent Diabetes Mellitus (IDDM), Type 1: pancreas does not produce insulin, condition is believed to be brought on by exposure to an environmental agent, causes immune cells to destroy the pancreatic islets

Hypoglycemia: either an overdose of insulin or missing a meal can bring on the symptoms of hypoglycemia (low blood sugar), symptoms include perspiration, pale skin, shallow breathing, and anxiety

Noninsulin-dependent Diabetes Mellitus (NIIDM), Type 2: usually occurs in people of any age who tend to be obese, amount of insulin in the blood of these patients is normal or elevated but the insulin receptors on the cells do not respond

Other Endocrine GlandsThere are several other glands in the Endocrine

System that also produce hormonesInclude:◦Gonads (ovaries in females, testes in males)◦Thymus Gland (lesser-known)◦Pineal Gland (lesser-known)

Few tissues within organs produce hormones or growth factors

Gonadotropic Hormone: stimulate the gonads to produce gametes and sex hormones

Ovaries and TestesHypothalamus and the Pituitary Gland control

hormonal secretions of these organs

Testes: located in scrotum◦Produce androgens (like testosterone) which are

the male sex hormones

Ovaries: located in pelvis cavity◦Produce estrogen/progesterone which are the

female sex hormones

Thymus and Pineal Glands Thymus Gland: lies beneath sternum, most active/largest during childhood

Lymphocytes: white blood cells which originate in the bone marrow and are responsible for certain defenses against specific invaders

Thymus-derived Lymphocytes (T-lymphocytes): what lymphocytes are transformed into once they pass complete development in the thymus

Thymosins: hormones that epithelial cells secrete that line the lobules of the thymus

Pineal Gland: located in brain, produces hormone known as melatonin – primarily at night

Melatonin: involved in our daily sleep-wake cycle; also regulates sexual development

Growth FactorsNumerous types of organs and cells produce peptide growth

factors (stimulate cell division and mitosis)

Granulocyte and Macrophage Colony-Stimulating Factor (GM-CSF): causes bone marrow stem cells to form granulocyte or macrophage cells which are forms of white blood cells/leukocytes

Platelet-Derived Growth Factor: released from platelets and form several other cell types; helps in wound healing

Epidermal Growth Factor and Nerve Growth Factor: important in wound healing

Tumor Angiogenesis Factor: stimulates creation of capillary networks, released by tumor cells

HomeostasisThe Endocrine Systems works together with

the Nervous System in order to maintain homeostasis

The Endocrine System helps regulate: digestion fuel metabolism blood pressure and volume calcium balance response to the external environment

Chemical SignalsChemical Signals: molecules that affect behavior of

cells that have receptor proteins to receive them

Prostaglandins: potent chemical signals produced within cells from arachidonate (which is a fatty acid)◦Local messenger chemicals that individual body

cells produce◦Not distributed in blood, act closely to where they

were produced – locally

Effects of AgingThyroid disorders/Diabetes: most significant

endocrine problems that affect our health and function as we age

Grave’s Disease: autoimmune disease that targets thyroid, symptoms of cardiovascular disease/increased body temperature/fatigue

Hypothyroidism/Hyperthyroidism: both seen in the elderly ◦Hypothyroidism (Myxedema) can fail to be diagnosed

since symptoms are confused with aging