Cell Communication & Homeostasis

Cell Communication & Homeostasis

• Cells communicate through chemical signals like hormones and neurotransmitters, as well as direct contact via gap junctions.
• These forms of communication maintain homeostasis by regulating bodily functions like temperature, pH and metabolism.

Nervous System vs. Endocrine System

• The nervous system produces a fast, short-term response using electrical signals and reflexes.
• The endocrine system produces a slow, long-term response using hormones that regulate growth and metabolism.

Hormone Functions & Classification

• Cells respond to hormones through receptors for specific hormones, which triggers a reaction like insulin lowering blood sugar
• Tropic hormones stimulate other glands; TSH stimulates the thyroid.
• Steroid hormones include cortisol, testosterone, and estrogen.
  • They pass through cell membranes to affect DNA.
• Peptide hormones like insulin are made from amino acids.
• Eicosanoids like prostaglandins are derived from fatty acids.
• Eicosanoids are made from arachidonic acid and include prostaglandins (inflammation) and leukotrienes (immune response).
• Hormones are classified as steroid (lipid-soluble), peptide (water-soluble), or amino acid-derived.
• Hormone secretion occurs via endocrine glands using feedback loops.

Hormone Action & Regulation

• Estrogen enters cells, binds to receptors, and influences gene expression.
• cAMP acts as a second messenger: hormone binds to receptor, which then activates G protein, which activates adenylate cyclase, which converts ATP to cAMP, which activates enzymes.

Key Terms

• Negative feedback inhibition describes how a hormone stops its own further release (e.g., insulin & glucose).
• Antagonistic effect describes when two hormones oppose each other (e.g., insulin & glucagon).
• Up-regulation occurs when more receptors present which yield a stronger response.
• Down-regulation occurs when fewer receptors are present which yield a weaker response.
• Enzyme amplification describes when one hormone molecule triggers many enzyme activations.

Endocrine System & Hormones

• Hormone's function regulate metabolism, growth, reproduction, mood, and immune function.
• Endocrine organs include the hypothalamus, pituitary, thyroid, pancreas, and adrenal glands.
• ADH (Vasopressin) contributes to water retention.

Hypothalamus & Pituitary Hormones

• The hypothalamus releases hormones that control the pituitary.
• The anterior pituitary releases GH (growth), TSH (thyroid), and ACTH (stress response).
• The posterior pituitary releases ADH (water balance), and oxytocin (labor).
• The pancreas secretes insulin (lowers glucose) and glucagon (raises glucose).
• The thyroid gland releases T3/T4 for metabolism and is transported via blood proteins.
• The pineal gland secretes melatonin to regulate the sleep cycle.

Signal Transduction

• Water-soluble hormones use second messengers.
• Lipid-soluble hormones enter cells directly.
• The hypothalamic-hypophyseal portal system describes the blood vessel network linking the hypothalamus and pituitary.
• Endocrine hormone regulation occurs through negative feedback, like thyroid hormone levels control TSH release.

Endocrine & Blood System

• Chief cells (parathyroid) produce PTH to balance calcium.
• Chromaffin cells (adrenal medulla) produces epinephrine for fight-or-flight responses.
• Parafollicular cells (thyroid) produce calcitonin to lower calcium.
• General Adaptation Syndrome describes the stress response stages: alarm, resistance, and exhaustion.

Endocrine Diseases

• Diabetes is characterized by high blood sugar.
• Graves' disease is characterized by an overactive thyroid.
• Cushing's syndrome is characterized by having too much cortisol.
• Goiter is describes an enlarged thyroid.
• Acromegaly is excess GH in adults.
• Addison's disease is low cortisol.
• Hypothyroidism is low thyroid hormone.

Disease Classification

• Primary diseases are due to an issue in the gland itself.
• Secondary diseases stem from an issue in the pituitary.
• Tertiary diseases stem from an issue in the hypothalamus.

Gland Functions

• The thymus’ functions include immune cell production.
• The thyroid’s function is to regulate metabolism.
• The adrenal’s function is for stress response.
• The pancreas’ function is to control blood sugar.
• The parathyroid’s function is to regulate calcium balance.

Blood Composition & Circulatory System

• Formed elements of blood include RBCs, WBCs, and platelets.
• Plasma consists of water, proteins, and nutrients.
• Serum is plasma without clotting factors.
• Albumin is a protein in plasma that maintains blood pressure.
• Hematocrit is the percentage of RBCs in blood.
• Anemia is low RBC counts which causes fatigue.
• Leukocytes include five types, neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
• Plasma is composed of water, electrolytes, and proteins.
• Lymphocytes provide immune response and have long lifespans.
• Leukopoiesis is WBC production in bone marrow.
• Hemopoietic stem cells are found in bone marrow.
• Sickle-cell anemia is a genetic disorder causing misshapen RBCs.

Feedback Mechanisms

• Positive feedback enhances change, such as labor contractions.
• Negative feedback reverses change, such as blood sugar regulation.
• RBCs have a biconcave shape, and hemoglobin carries oxygen.
• Gas transport includes RBCs carrying oxygen (O2) and carbon dioxide (CO2).
• The liver and spleen break down old RBCs.
• Hematopoiesis is RBC formation regulated by EPO in the kidneys.
• Blood types include A, B, AB, and O (with Rh factor).
• Rh incompatibility describes when an Rh- mother with Rh+ baby leads to possible complications.
• The universal donor is O-.
• The universal recipient is AB+.
• Hemolytic disease of newborn describes when mother's antibodies attack baby's RBCs.
• Platelets aid in clotting.
• The clotting cascade describes the cascade of steps leading to blood clot formation.
• Blood viscosity is the thickness of blood and is affected by RBCs and plasma proteins.
• Hemoglobin breaks down in the liver and spleen.
• Lymphoid hemopoiesis occurs in lymphatic organs.
• EPO production is released by kidneys to stimulate RBCs.
• Thrombus is a stationary clot.
• Embolus is a moving clot.