Study Guide: Endocrine System, Blood, and Special Senses (BIOL 2404)

Endocrine System

Chemistry of Hormones

The endocrine system regulates bodily functions through the secretion of hormones, which are chemical messengers produced by glands and transported in the bloodstream to target organs.

• Peptide hormones: Short chains of amino acids; water-soluble; act via cell surface receptors.

• Amine hormones: Derived from amino acids (e.g., epinephrine); often act quickly.

• Protein hormones: Longer chains of amino acids; similar in action to peptide hormones.

• Steroid hormones: Derived from cholesterol; lipid-soluble; act via intracellular receptors.

Example: Insulin (peptide hormone) regulates blood glucose levels.

Second Messenger System

Many hormones use a second messenger system to transmit their signal inside target cells. The hormone binds to a receptor, activating a cascade that amplifies the signal.

• Key second messenger: Cyclic AMP (cAMP)

• Process: Hormone binds receptor → activates G protein → stimulates adenylate cyclase → increases cAMP → activates protein kinases

Stimuli for Hormone Release

Hormone release is controlled by various stimuli:

• Humoral: Changes in blood levels of ions/nutrients

• Neural: Nerve impulses stimulate release

• Hormonal: Other hormones stimulate release (tropic hormones)

Tropic Hormones

Tropic hormones stimulate other endocrine glands to release their hormones.

• Example: Thyroid-stimulating hormone (TSH) stimulates the thyroid gland.

Adrenal Cortex and Medulla

The adrenal gland has two main regions:

• Adrenal cortex: Produces steroid hormones (e.g., cortisol, aldosterone)

• Adrenal medulla: Produces catecholamines (e.g., epinephrine, norepinephrine)

Effects of catecholamines: Increased heart rate, blood pressure, and energy availability.

Pancreas and Hormones

The pancreas produces hormones that regulate blood glucose:

• Insulin: Lowers blood glucose

• Glucagon: Raises blood glucose

Gonads, Placenta, and Adrenal Medulla

These organs produce hormones essential for reproduction and stress response.

• Gonads: Produce sex hormones (e.g., estrogen, testosterone)

• Placenta: Produces hormones during pregnancy

• Adrenal medulla: Produces catecholamines

Blood

Composition and Functions of Blood

Blood is a connective tissue composed of plasma and formed elements. It transports nutrients, gases, wastes, and hormones.

• Plasma: Liquid component; contains water, proteins, nutrients, hormones

• Formed elements: Erythrocytes (red blood cells), leukocytes (white blood cells), platelets

• Buffy coat: Layer between plasma and red cells; contains white blood cells and platelets

Relative Abundance of Formed Elements

• Erythrocytes: Most abundant

• Leukocytes: Less abundant

• Platelets: Least abundant

Erythrocytes

Erythrocytes (red blood cells) transport oxygen using hemoglobin.

• Shape: Biconcave

• Function: Oxygen transport

Homeostatic Imbalance

Imbalances in blood composition can lead to disorders such as anemia, polycythemia, or leukopenia.

Granulocytes and Agranulocytes

White blood cells are classified based on the presence of granules:

• Granulocytes: Neutrophils, eosinophils, basophils

• Agranulocytes: Lymphocytes, monocytes

Platelets

Platelets are cell fragments involved in blood clotting.

Hematopoiesis

Hematopoiesis is the process of blood cell formation, occurring in the bone marrow.

Hemostasis

Hemostasis is the process that stops bleeding:

• Vascular spasm

• Platelet plug formation

• Coagulation (clotting)

Anticoagulants

Anticoagulants prevent blood clotting and are used to reduce the risk of thrombosis.

Blood Groups and Transfusions

Blood groups are determined by antigens on red blood cells. Safe transfusions require compatibility between donor and recipient blood types.

• Major blood groups: A, B, AB, O

• Rh factor: Positive or negative

Special Senses (Extra Credit)

Internal Structures of the Eyeball

The eyeball contains several internal structures essential for vision:

• Cornea: Transparent front layer

• Lens: Focuses light

• Retina: Contains photoreceptors

Visual Fields and Pathways

Visual information is processed through specific pathways from the retina to the brain.

• Optic nerve: Transmits signals to the brain

• Visual fields: Areas seen by each eye

Photoreceptor Cells

Photoreceptors in the retina detect light:

• Rods: Sensitive to dim light

• Cones: Detect color

Structures Involved in Hearing

Hearing involves the transmission of sound waves through the ear to the cochlear nerve.

• Outer ear: Collects sound

• Middle ear: Transmits vibrations

• Inner ear: Contains cochlea and spiral organ of Corti

Spiral Organ of Corti

The spiral organ of Corti is the main hearing organ, converting vibrations into nerve impulses.

Static and Dynamic Equilibrium

Equilibrium is maintained by structures in the inner ear:

• Static equilibrium: Sensed by vestibule

• Dynamic equilibrium: Sensed by semicircular canals

Primary Taste Sensations and Gustatory Hairs

Taste is detected by taste buds, which contain gustatory hairs that sense chemicals.

• Primary taste sensations: Sweet, sour, salty, bitter, umami

• Gustatory hairs: Microvilli that detect taste molecules

Papillae

Papillae are structures on the tongue that contain taste buds.

• Types: Filiform, fungiform, circumvallate