Chapter 20 Endocrine System

Fig. 20.1 Endocrine glands transmit signals through blood stream to cells far away Different from nervous system; Neuron can affect only cells it contacts Endocrine gland Neuron Hormone Nerve signal Blood Target cells Target cells Neurotransmitter (a) Nervous system (b) Endocrine system

Fig. 20.2 Major endocrine glands Organs containing endocrine cells Hypothalamus Pituitary gland Pineal gland Thymus Heart Thyroid gland Kidney Gastrointestinal (GI) tract Pancreatic islets Parathyroid glands Adrenal glands

Fig. 20.4 Hypothalamus The hypothalamus produces regulatory hormones that either stimulate or inhibit anterior pituitary hormone secretion. The hypothalamus produces two hormones (antidiuretic hormone and oxytocin) that are stored in and released from the posterior pituitary. Anterior pituitary Posterior pituitary

Adrenal glucocorticoids Adrenal cortex Adrenal cortex secretes three types of steroid hormones Aldosterone (aka mineralocorticoid) Glucocorticoids, including cortisol Increase plasma glucose concentrations Sex hormones, including estrogens, progesterone, and androgens DHEA (dietary supplement) converted to testosterone Kidney

Growth hormone Released by anterior pituitary throughout life Anabolic Hypothalamus Released by anterior pituitary throughout life Anabolic Required for growth in childhood Combined with thyroid, insulin, sex hormones in some cases In adults, GH stimulates release of insulin-like growth factors (IGF) Stimulate bone and soft tissue growth Anterior pituitary Posterior pituitary

Growth hormone pathologies In childhood, lack of GH leads to dwarfism with proportional body (one of many possible causes of dwarfism)

Growth hormone pathologies Excessive GH leads to acromegaly Long jaw, coarse facial features, excessive height

Thyroid In adults: In children Increase oxygen consumption in tissues Larynx Thyroid gland Trachea Thyroid In adults: Increase oxygen consumption in tissues Modulate metabolism of proteins, carbohydrates, and fat In children Necessary for expression of growth hormone Necessary for development of nervous system Figure 23.4 (2 of 6) 9

Fig. 20.11 Hypothalamus secretes thyrotropin-releasing hormone (TRH), which acts on the anterior pituitary. Hypothalamus stimulatory inhibitory Negative feedback inhibition TRH Anterior pituitary TSH Anterior pituitary releases thyroid-stimulating hormone (TSH). Thyroid gland releases thyroid hormone (TH). TH Target cells increase metabolic activities. Target organs in body Secretion of TRH by the hypothalamus is inhibited. TH prevents the formation of TSH in anterior pituitary 1 2 3 4 5

Hyperthyroidism Elevated TSH causes enlargement of thyroid gland = goiter Increases oxygen consumption and metabolic heat production Causes warm, sweaty skin; intolerance to heat Protein catabolism causes weak muscles Weight loss Hyperexcitable reflexes Insomnia, irritability, psychosis Rapid heartbeat

Hyperthyroidism Graves’ disease Body produces antibodies that mimic TSH Thyroid overstimulated May cause exophthalmos (bulging eyes) Caused by enlargement of tissues around eyes Marty Feldman

Parathyroid gland Regulates calcium levels in the blood vital for muscle contractions

Pancreas Located behind stomach Fig. 20.15 Body of pancreas Spleen Pancreatic ducts Tail of pancreas Major duodenal papilla Duodenum of small intestine Head of pancreas

Pancreas Acinar cells produce digestive juices (not endocrine) Fig. 20.15 Fig. 20.15 Pancreas Blood capillary Acinar cells produce digestive juices (not endocrine) Pancreatic islets are clusters of endocrine cells Delta cell F cell Pancreatic islet cells Alpha cell Beta cell Pancreatic acinus Alpha cell Beta cell Delta cell F cell Pancreatic islet

Pancreas Alpha cells secrete glucagon when blood glucose is low Fig. 20.15 Fig. 20.15 Pancreas Blood capillary Alpha cells secrete glucagon when blood glucose is low Beta cells secrete insulin when blood glucose is high Delta cells and F cells affect digestion and release of insulin and glucagon Delta cell F cell Pancreatic islet cells Alpha cell Beta cell Pancreatic acinus Alpha cell Beta cell Delta cell F cell Pancreatic islet