Animal Coordination Chemical Regulation

Endocrine vs Exocrine secretion

THE NATURE OF CHEMICAL REGULATION Chemical signals coordinate activities in different parts of the body Hormones are chemical signals, usually carried in the blood Bind to receptors on / in target cells Cause specific changes in target cells Exert effects at very low concentrations

The Chemistry of Hormones Amino acid-based hormones Proteins Peptides Amines Steroids – made from cholesterol Prostaglandins – made from highly active lipids

Hormones are secreted by Endocrine glands and neurosecretory cells Secretory vesicles Endocrine cell Hormone molecules Blood vessel Target cell Neurosecretory cell Hormone molecules Blood vessel Target cell

A few chemicals serve both as hormones in the endocrine system And as chemical signals in the nervous system Nerve cell Nerve signals Neurotransmitter molecules

Mechanisms of Hormone Action Hormones affect only certain tissues or organs (target cells or organs) Target cells must have specific protein receptors Hormone binding influences the working of the cells Slide 9.4

Effects Caused by Hormones Changes in plasma membrane permeability or electrical state Synthesis of proteins, such as enzymes Activation or inactivation of enzymes Stimulation of mitosis Slide 9.5

Mechanisms of Hormone Action Hormones affect target cells by two main signaling mechanisms depending on whether it can pass through the plasma membrane Steroid hormones ( fat soluble) Non-Steroid hormones (water soluble)

Steroid Hormone Action Lipid-soluble hormone (testosterone) Target cell Receptor protein Hormone- receptor complex Nucleus DNA mRNA Transcription New protein Cellular response: activation of a gene and synthesis of new protein Steroid hormones, such as the sex hormones estrogen and testosterone: Diffuse through the plasma membrane of target cells (how?) Bind to intracellular receptors Hormone receptor complex binds DNA in nucleus Activate genes thus initiates transcription 1 2 3 4

Steroid Hormone Action Diffuse through the plasma membrane of target cells (how?) Enter the nucleus Bind to a specific protein within the nucleus Bind to specific sites on the cell’s DNA Activate genes that result in synthesis of new proteins Slide 9.6

Steroid Hormone Action Figure 9.1a Slide 9.7

Nonsteroid Hormone Action Hormone binds to a membrane receptor Hormone does not enter the cell Sets off a series of reactions that activates an enzyme Catalyzes a reaction that produces a second messenger molecule Oversees additional intracellular changes to promote a specific response Slide 9.8

Nonsteroid Hormone Action Water-soluble hormones such as proteins and amines Bind to plasma-membrane receptors on target cells Figure 9.1b Slide 9.9

Signal transduction pathway for non-steroid hormones Hormone binds to a receptor protein on the plasma membrane Receptor protein activates a signal-transduction pathway in the cell Series of relay molecules transmits the signal to a protein that carries out the cell’s response

Control of Hormone Release Hormone levels in the blood are maintained by negative feedback A stimulus or low hormone levels in the blood triggers the release of more hormone Hormone release stops once an appropriate level in the blood is reached Slide 9.10

Hormonal Stimuli of Endocrine Glands Endocrine glands are activated by other hormones Figure 9.2a Slide 9.11

Chemical Stimuli of Endocrine Glands Changing blood levels of certain ions / metabolite stimulate hormone release Figure 9.2b Slide 9.12

Neural Stimuli of Endocrine Glands Nerve impulses stimulate hormone release Most are under control of the sympathetic nervous system Figure 9.2c Slide 9.13

26.3 Overview: The vertebrate endocrine system Consists of more than a dozen glands secreting more than 50 hormones Hypothalamus Pineal gland Pituitary gland Thyroid gland Parathyroid glands Thymus Adrenal glands (atop kidneys) Pancreas Ovary (female) Testes (male) Figure 26.3

Location of Major Endrocrine Organs Figure 9.3 Slide 9.14

26.4 The hypothalamus, closely tied to the pituitary, connects the nervous and endocrine systems The hypothalamus exerts master control over the endocrine system By using the pituitary gland to relay directives to other glands Brain Posterior pituitary Anterior pituitary Bone Hypothalamus

Posterior pituitary Anterior pituitary Composed of nervous tissue Stores and secretes hormones made in the hypothalamus Anterior pituitary Composed of glandular tissue Hormone release controlled by releasing hormones – under control of the hypothalamus Control the secretion of other hormones by producing trophic hormones.

The posterior pituitary The posterior pituitary Secretes oxytocin and antidiuretic hormone (ADH) Hypothalamus transmits nerve signals that trigger release from posterior pituitary Hypothalamus Neurosecretory cell Hormone Posterior pituitary Blood vessel Oxytocin ADH Uterine muscles Mammary glands Kidney tubules Anterior

The posterior pituitary (neurohypo- physis) stores and secretes hormones produced by the hypothalamus.

The anterior pituitary Releasing and inhibiting hormones secreted by the hypothalamus control the anterior pituitary Portal system The anterior pituitary Secretes TSH, ACTH, FSH and LH, growth hormone, prolactin.

too little GH or defective receptors Growth hormone disorder Children too little GH or defective receptors dwarfism too much GH gigantism

ACROMEGALY

Table 45.1 (continued)

Secretion of thyroxine by the thyroid gland Hypothalamus Inhibition TRH Anterior pituitary Thyroid TSH Thyroxine Secretion of thyroxine by the thyroid gland Is controlled by a negative-feedback mechanism

HORMONES AND HOMEOSTASIS The thyroid regulates development and metabolism Two hormones from the thyroid gland, T4 and T3 Regulate an animal’s development and metabolism

Thyroid imbalance Can cause cretinism, metabolic disorders and goiter

Maintains homeostatic levels of T4 and T3 in the blood Negative feedback Maintains homeostatic levels of T4 and T3 in the blood Hypothalamus Anterior pituitary Thyroid No inhibition No iodine Insufficient T4 and T3 produced Thyroid grows to form goiter TRH TSH

Pancreatic hormones Pancreatic hormones regulate blood glucose levels Pancreatic hormones regulate blood glucose levels The pancreas secretes two hormones Insulin Signals cells to use and store glucose Glucagon Signals cells to release stored glucose into the blood

http://www.sunyniagara.cc.ny.us/val/pancreas2.jpg

The islets are composed of three cell types: alpha cells, beta cells, and delta cells. These cells cannot be readily distinguished without special stains. Delta cells (not visibly stained in this slide) are found throughout the islet and secrete somatostatin. The insulin producing cells are called  cells and make up about 70% of the islet cells. The glucagon producing cells are called  cells and make up about 15 - 20% of the islet cells. http://www.cytochemistry.net/microanatomy/Endocrines/pancreas2.jpg

 cells of islets of Langerhans SECRETORY ROLE CELL CHARACTERISTICS  cells of islets of Langerhans Glucagon 15 - 20% of the islet cells; generally more peripherally located in the islet; more uniform in size; cytoplasm appears to be more densely packed than the  cells  cells of islets of Langerhans Insulin 70% of the islet cells; generally more centrally located in the islet  cells of islets of Langerhans Somatostatin approximately 5 – 10% of the islets Acinus cells Digestive enzymes Usually oriented in a circular pattern

Homeostasis: Normal blood glucose level Glucose balance Body cells take up more glucose Insulin Blood glucose level declines to a set point; stimulus for insulin release diminishes Stimulus: Declining blood glucose level (e.g., after skipping a meal) Alpha cells of pancreas stimulated to release glucagon into the blood Glucagon Liver breaks down glycogen and releases glucose to the blood Blood glucose level rises to set point; stimulus for glucagon release diminishes Rising blood glucose level (e.g., after eating a carbohydrate-rich meal) Homeostasis: Normal blood glucose level (about 90 mg/100mL) Beta cells of pancreas stimulated to release insulin into the blood Liver takes up glucose and stores it as glycogen High blood glucose level

Hours after glucose ingestion Diabetes can be detected By a test called a glucose tolerance test 400 350 300 Diabetic Blood glucose (mg/100mL) 250 200 150 100 Normal 50 1 2 1 2 3 4 5 Hours after glucose ingestion

Diabetes is a common endocrine disorder Diabetes mellitus Results from a lack of insulin or a failure of cells to respond to it 2 types of diabetes Type I (insulin-dependent) Autoimmune disease Beta cells destroyed, no insulin made Type II Body cells fail to respond to insulin

Diabetes type I and type II Type II - due to aging, lifestyle, heredity and other lifestyle (diet) factors decreased responsiveness by cells of target organs to insulin Type I - autoimmune disorder (destroys ability to produce insulin)

Complications related to Diabetes

Insulin Pump

Interaction between Hormones synergism occurs when more than one hormone produces the same effects in a target cell, and their combined effects are amplified both glucagon and epinephrine cause the liver to release glucose into the bloodstream 2. antagonism occurs when one hormone opposes the action of another hormone insulin lowers blood sugar, and glucagon raises blood sugar

Adrenal glands consists of adrenal cortex and adrenal medulla

The adrenal glands mobilize responses to stress The adrenal glands mobilize responses to stress Hormones from the adrenal glands Help maintain homeostasis when the body is stressed Adrenal medulla Nervous signals from hypothalamus stimulate secretion of epinephrine Trigger fight or flight response

Boost blood pressure and energy in response to long-term stress Adrenal cortex ACTH from the pituitary causes the adrenal cortex to secrete glucocorticoids and mineralocorticoids Boost blood pressure and energy in response to long-term stress

How the adrenal glands control our responses to stress Figure 26.9

Glucocorticoids offer relief from pain, but not without serious risks Glucocorticoids relieve inflammation and pain But they can mask injury and suppress immunity Figure 26.10

The gonads secrete sex hormones Estrogens, progestins, and androgens are steroid sex hormones Produced by the gonads in response to signals from the hypothalamus and pituitary Estrogen and progestins Maintain female reproductive system Development of female characteristics

Androgens, such as testosterone Androgens, such as testosterone Trigger the development of male characteristics

Other Hormone-Producing Structures a. Gastrointestinal tract contains enteroendocrine cells throughout the mucosa secrete hormones to regulate digestive functions b. Placenta secretes estrogens, progesterone, and human chorionic gonadotropin act on the uterus to influence pregnancy

Other Hormone-Producing Structures c. Kidneys produce erythropoietin--signals the bone marrow to make RBCs d. Skin produces cholecalciferol--inactive form of vitamin D3 e. Adipose tissue produces leptin---acts on the hypothalamus to produce a feeling of satiety

Hypothalamic feeding center Neuropeptide Y Hypothalamic feeding center Negative feedback  Food intake  Fat stores     Leptin secretion   

Hypothalamic feeding center Neuropeptide Y Hypothalamic feeding center X Negative feedback  Food intake  Fat stores    X  Leptin secretion