Chapter 45 Hormones and the Endocrine System

Tissue Communication Extracellular animals have multiple levels of tissue organization. Communication is essential to maintain homeostasis. Endotherms vs ectotherms Bioregulators are used.

The thermostat function of the hypothalamus and feedback mechanisms in human thermoregulation

Chemical Signals Used for tissue communication Secreted chemical signals include –Local regulators (travel short distances via diffusion) –Neurotransmitters (nervous or endocrine communication) –Hormones (secreted into bloodstream, travel long distances) –Neurohormones (nerves that secrete hormones)

Types of Cellular Action __________ – impacting yourself. __________– impacting your neighbors. __________– impacting the next nerve in sequence. Short distance, quick communication. __________– chemical secreted into blood stream. Impacts distant targets, longer lasting communication. __________– neurons secrete hormones into bloodstream.

Fig Blood vessel Response (a) Endocrine signaling (b) Paracrine signaling (c) Autocrine signaling (d) Synaptic signaling Neuron Neurosecretory cell (e) Neuroendocrine signaling Blood vessel Synapse Response

Integration of Systems Hormones impact the body through interrelationships of the __________ system and the __________ system. The endocrine system secretes hormones that coordinate __________, but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior. The nervous system conveys __________ electrical signals along specialized cells called neurons; these signals regulate other cells. NOTE: Some neurons can secrete hormones…

Neurotransmitters Neurons (nerve cells) contact target cells at __________. At synapses, neurons secrete chemical signals called __________ that diffuse a short distance to bind to receptors on the target cell. Neurotransmitters play a role in sensation, memory, cognition, and movement. Many neurotransmitters can also serve as __________. –Example: Epinephrine ( __________ ) during ‘fight or flight’ response Neuron Synapse Response

The Body’s Long-Distance Regulators Animal __________ are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body. Hormones mediate responses to environmental stimuli and regulate growth, development, and reproduction. Stimuli can include: –Change in __________ –Another __________ –__________ impulses –__________ cues

Neurohormones Nerves that secrete hormones into the __________. Have long-lasting effects at distant targets. Can store hormones (weird) Examples: hypothalamic hormones, oxytocin, anti- diuretic hormone Neurosecretory cell Response Blood vessel

How Hormones Work… Three part system: –1. Hormone is secreted –2. Travels to distant targets via bloodstream –3. Bind at specific target cells and cause a specific response Endocrine glands are: –Ductless glands, secretory cells –Well vascularized –Range in size from individual cells to entire organs Secretion can be turned off or amplified via feedback loops

Feedback Mechanisms: Negative The goal is to get back to the ‘norm’. Something in the body needs to be amended  hormone secreted from endocrine tissue  travels to target tissue  target response deals with situation, levels rise, etc. and shuts down further hormone secretion from endocrine tissue.

Fig Homeostasis: Blood glucose level (about 90 mg/100 mL) Insulin Beta cells of pancreas release insulin into the blood. STIMULUS: Blood glucose level rises. Liver takes up glucose and stores it as glycogen. Blood glucose level declines. Body cells take up more glucose.

Feedback Mechanisms: Positive The goal is to bring about ‘change’ Endocrine tissue secretes hormone  hormone impacts target tissue, elicits response  causes greater production of original endocrine tissue

Fig Suckling Pathway Stimulus Hypothalamus/ posterior pituitary Positive feedback Example Sensory neuron Neurosecretory cell Blood vessel Posterior pituitary secretes oxytocin ( ) Target cells Response Smooth muscle in breasts Milk release +

Fig Major endocrine glands: Adrenal glands Hypothalamus Pineal gland Pituitary gland Thyroid gland Parathyroid glands Pancreas Kidney Ovaries Testes Organs containing endocrine cells: Thymus Heart Liver Stomach Kidney Small intestine

A few hormones…

and a few more…

Let’s simplify a bit… Chemical Classes of Hormones Three major classes of molecules function as hormones in vertebrates: –__________(proteins and peptides) –Amines derived from __________ –__________ hormones

Protein (or peptide) Hormones Made from proteins (hydrophilic) 2 categories: –Monoamines-made from one amino acid (lots of neurotransmitters, such as epinephrine) –Polypeptides-made from multiple amino acids. Examples: Growth Hormone, Insulin Bind to membrane-bound receptors, use intracellular second messengers for response Can bring about a quick response Secreted from: –Pituitary –Pancreas –Parathyroid

Steroid Hormones Made from lipids All are derived from cholesterol Made within: a. Gonads (testosterone, estrogen) b. Adrenals (cortisol, aldosterone) c. Brain (???) Bind to intracellular receptors Influence gene formation Impacts: –Metabolism –Gamete formation –Stress response –Growth –Sex characteristics –Behavior

Coordination of Endocrine and Nervous Systems in Vertebrates The hypothalamus receives information from the nervous system and initiates responses through the endocrine system. It turns neural input into hormonal output through neurohormone secretions. Examples: Gonadotropin releasing hormone (GnRH) Thyrotropin releasing hormone (TRH) Attached to the hypothalamus is the pituitary gland composed of the anterior pituitary and posterior pituitary. Together, these structures regulate lots of hormonal processes.

Fig Spinal cord Posterior pituitary Cerebellum Pineal gland Anterior pituitary Hypothalamus Pituitary gland Hypothalamus Thalamus Cerebrum

The anterior pituitary makes and releases peptide hormones into the bloodstream under regulation of the hypothalamus. The anterior pituitary releases a new hormone in response to having received one by the hypothalamus. These hormones impact a variety of targets. Examples: Follicle stimulating hormone (FSH) Luteinizing hormone (LH) Adrenocorticotropic hormone (ACTH) Anterior Pituitary

Posterior Pituitary Hormones The posterior pituitary stores and secretes hormones that are made in the hypothalamus. These are neurohormones. Two hormones released from the posterior pituitary act directly on nonendocrine tissues. –Oxytocin (OT) induces uterine contractions and the release of milk –Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

Fig Posterior pituitary Anterior pituitary Neurosecretory cells of the hypothalamus Hypothalamus Axon HORMONE Oxytocin ADH Kidney tubulesTARGETMammary glands, uterine muscles

Endocrine GlandWhat it does… Pineal glandServes as biological clock ThyroidRegulates metabolism ParathyroidCalcium regulation AdrenalsStress coping, ion regulation Pancreas (certain cells)Glucose regulation GonadsGamete formation, behavior Plus many, many, many more….. Some examples:

A practical application: Diabetes mellitus Diabetes mellitus is perhaps the best-known endocrine disorder. It is caused by a deficiency of insulin (Type I) or a decreased response to insulin in target tissues (Type II). –Type I = usually genetic –Type II = lifestyle induced, some genetic influence It is marked by elevated blood glucose levels. –Used to be assessed through urine tasting (yuck!)

Insulin and Glucagon: Control of Blood Glucose Diabetes results in the inability to effectively regulate glucose levels. Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis. The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin.

Target Tissues for Insulin and Glucagon Insulin reduces blood glucose levels by: –Promoting the cellular uptake of glucose –Slowing glycogen breakdown in the liver –Promoting fat storage Glucagon increases blood glucose levels by: –Stimulating conversion of glycogen to glucose in the liver –Stimulating breakdown of fat and protein into glucose

Fig Homeostasis: Blood glucose level (about 90 mg/100 mL) Glucagon STIMULUS: Blood glucose level falls. Alpha cells of pancreas release glucagon. Liver breaks down glycogen and releases glucose. Blood glucose level rises. STIMULUS: Blood glucose level rises. Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. Blood glucose level declines. Body cells take up more glucose. Insulin

Other Applications: Gamete Production Secondary Sex Characteristics Birth Control Aggression