Physiology Exam Study Guide #3 (ch 11, 13, 14, 16)

Ch 11

Endocrine Glands

• System of endocrine glands and cells that secrete hormone

  • A major physiological control system

Gland: 

• A group of epithelial cell or an organ that synthesizes and secretes chemical substances

  • Endocrine glands are ductless, and secrete hormones into bloodstream, to travel to target cell

  • Exocrine glands have ducts

Hormone:

• A biologically active molecule that serves as a chemical messenger in the blood 

  • Secreted by gland or cell and then carried through blood receptors on target cells, causing a response

  • Receptor is in plasma membrane for polar hormones

  • Receptor is in cytoplasm for nonpolar hormones

Major Endocrine Glands

• Pituitary gland

• Pineal gland

• Hypothalamus

• Thyroid gland

• Adrenal gland

• Ovary testis

• Pancreas

Four Chemical Structure of Hormones

• Amine Hormones

  1. Derive from tyrosine and tryptophan (AAs)

  2. EX: thyroid hormones, E and NE, dopamine, melatonin

• Polypeptide and Protein Hormone

  1. Most hormones, many sites

  2. EX: antidiuretic hormone (ADH), growth hormone (GH), insulin, oxytocin, glucagon, adrenocorticotropic hormone (ACTH)

• Glycoproteins

  1. Protein bound to carbohydrate

  2. EX: thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH)

• Steroids 

  1. Lipids based on cholesterol

  2. EX: testosterone, estrogen, progesterone, aldosterone, cortisol

Control of Hormone Secretion 

• Three types of input to endocrine cells can stimulate or inhibit hormone secretion, and multiple inputs can be active simultaneously:

1. Concentration of ions or nutrients:

   1. Hormone regulates plasma concentration of the ion or nutrient via negative feedback

   2. EX: insulin lowers blood glucose concentration

2. Nervous System:

   1. Autonomic NS controls adrenal medulla and other endocrine glands

      1. EX: insulin secretion stimulated by parasympathetic NS and inhibited by Sympathetic NS

   2. Hypothalamus & posterior pituitary hormones are directly regulated by neurons of the brain 

3. Hormones:

   1. Secretion of a hormone can be directly regulated by blood concentration of another hormone, called a Tropicor trophic hormone. This is a hormone that stimulates secretion of another hormone

      1. EX: the gonadotropic hormone LH stimulates secretion of testosterone by the testes

Pituitary Gland (Hypophysis)

Posterior pituitary hormones

Two hormone:

• Oxytocin: stimulates smooth muscle in mammary gland and uterus (reproductive)

• Antidiuretic hormone (ADH) or vasopressin: acts on smooth muscle in blood vessels to increase blood pressure (constriction) and acts on kidney to retain fluids for blood volume (circulatory, renal)

• Synthesised in hypothalamus

• Axons of hypothalamic-hypophyseal tract terminate on capillaries in posterior pituitary gland, where hormones are released in the bloodstream 

The posterior pituitary gland store and releases hormone that are synthesized in the hypothalamus 

• Hormones are transported into capillaries in the posterior pituitary via the axons in the hypothalamo-hypophyseal tract 

Anterior Pituitary Hormones

• Six hormones and their targets 

• Have a trophic effect: hormones secreted by anterior pituitary gland stimulate secretion of another hormone 

• There is usually a 3-hormone sequence

  • Hypothalamic hormone (1) is secreted from the hypothalamic neuron into the hypothalamo-hypophyseal portal system, to control the secretion of…

  • An anterior pituitary hormone (2) (tropic hormone), which controls secretion of…

  • A hormone (3) from another endocrine gland, which affects target cells

    • OR (2) is a physiology response

• Hypothalamic hormones (green) from the hypothalamus are transported to the anterior pituitary gland via the blood vessels of hypothalamo-hypophyseal portal system

• Upon arrival, the hypothalamic hormones bind to receptors on the anterior pituitary cells to evoke secretion of the anterior pituitary hormones (red, tropic hormones) into the same capillaries -> blood circulation 

Hypothalamus-pituitary-gonad axis

• Hypothalamus creates hormone

  • Gonadotropin releasing hormone (GnRh)

• Anterior pituitary gland

  • Gonadotropins (FSH and LH)

• Gonads

  • Sex steroids hormones (estrogen and androgens

  • ADrenal Glands & stress Response 

Stress

• Real or perceived threat to homeostasis

  • EX: emotional stress, pain, physical trauma, prolonged exposure to cold, decreased to water intake, sleep deprivation, infection, goregin

  • Cortisol, a glucose (steroid hormone) secreted by the adrenal cortex)

    • Differential renal tissues of the brain 

    • Help maintain blood pressure

    • Anti-inflammatory & auto-immune functions to control overactivity of immune system \Increases blood sugar level, decreases immune response

• Epinephrine, a catecholamine secreted they adrenal medulla 

• Increases heart rate & respiratory rate 

• Shifts blood flow to skeletal muscles 

Thyroid Glands

• The thyroid gland straddles the esophagus, just below the larynx, in the neck. It has two lobes

• The numerous microscopic thyroid follicles are filled with colloid, a protein-rich fluid, and are lined with follicular cells that synthesize T3 and T4

Hypothalamus-Pituitary-thyroid Axis

Three hormone sequence:

• TRH (hypothalamus)

• TSH (anterior pituitary)

• T3/T4 (thyroid glands) and thyroid

Thyroid follicle

Produce two hormones that can contain iodide: triiodothyronine (T3) and thyroxine (T4)

1. Iodise (I-) from ISF enters colloid, where it is oxidized and attached to the tyrosine fringe of (thyroglobulin) and (diiodotyrosine) 

2. Enzymes modify the structure of MIT and DIT and  couple them together:

   1. T3 test results from one MIT attached to one DIT (so there are 3 iodine)

   2. T4 results from two DITs coupled (so there are 4 iodides)

3. TG containing t# and T4 enters follicular cells via endocytosis (fluid endocytosis)

4. 4 T3 and T4 are released from Tg due to enzymes

5. T3 and T4 are secreted via diffusion into ISF

Actions of Thyroid Hormone

• Stimulates carbohydrate absorption from small intestine = energy for metabolism 

• Increases fatty acid release from adipocytes = energy for metabolism 

• Calorigenic (heat-generating) action = for temperature homeostasis

Clinical Examples

Hypothyroidism: 

• Lower than normal plasma concentration of T3 and T4

  • Symptoms include cold tolerance, weight gain, and lethargy due to decreased metabolic rate

  • In the US, usually due to Hashimoto’s disease, in which antibodies attack the thyroid gland

  • Can also result from iodine deficiency in the diet, which reduces synthesis of T3 and T4

  • Decreased T3 and T4 -> reduced negative feedback on the pituitary -> increased TSH-> enlarged thyroid or goiter due to overstimulation of thyroid gland

Iodine Deficiency 

• Insufficient dietary iodine inhibits negative feedback control of TSH secretion. This results in excess TSH and hypertrophy of the thyroid gland

Clinical Example

• Hyperthyroidism: greater than normal plasma concentration of T3 and T4

  • Symptoms include heat intolerance, weight loss, and possibly goiter

  • May be a result of hormone-secreting tumors of the thyroid, or an autoimmune disease called Graves’ disease

    • In Graves’ disease, antibodies act like TSH, stimulating the thyroid gland to grow and over secrete t3 and T4

Ch 13

Blood, Heart and Circulation 

Circulatory System 

• Circulatory system 

  • Organ system that transports molecules and other substances rapidly over long distances, between cells, tissues, and organs

    • Division: cardiovascular system. Lymphatic system 

  • Cardiovascular

    • Heart:

      • Pump of variable rate and strength

    • Vessels/Vascular System 

      • Pipes of variable diameter

      • Interconnected system

    • Blood 

      • Fluid (connective tissue) of variable volume and viscosity

      • Contains water, solutes, and cells

      • Average 5.5 L

Composition of Blood

• The hematocrit is a rapid assessment of blood composition. It is the percent of blood volume that is composed of red blood cells (RBCs or erythrocytes). Hemoglobin in RBCs carries O2 tissues and CO2 away from tissues

• Plasma, the fluid portion of blood, includes water, ions, protein, nutrients, gasses, hormone, wastes, ect.

• White blood cells

  • *WBSs or leukocytes”

  • For immunity

• Platelets

  • Cell fragments for clotting 

Circulation 

• The heart is the muscular pump that propels the blood through pulmonary (lung) circulation and systemic (other organs & tissues) circulation 

• Red color indicates blood is fully oxygenated due to its passing through the lungs

• Blue color indicates the blood is partially oxygenated due to its delivery of O2 to the cells 

The Heart

• Muscular organ : cardiac muscle + endothelial cells

  • Myocardium: muscular tissue of heart

  • Each cardiac muscle cell contracts with a heart beat

• Pumping action of the heart due to muscle contraction creates pressure to move blood quickly throughout the body 

• Right and left sides of heat separated by Septum 

• Ventricle: lower chamber of the heart, pumps blood into arteries

  • Right ventricle pumps blood to the lungs (via pulmonary arteries), pulmonary circulation 

  • Left ventricle pumps oxygenated blood to the other tissues (via aorta), systemic circulation 

  • Interventricular septum separates the two ventricles

• Atrium: upper chamber of the heart, receives blood returning to hear

  • Right atrium receives blood from systemic circulation (via venae cavae)

  • Left atrium receives blood from pulmonary circulation (via pulmonary veins).

• Atrium and ventricle separated by connective tissue, fibrous skeleton 

Pulmonary & Systemic Circulation 

• Pulmonary Circulation:

  • Circuit through which partially oxygenated blood travels from the right ventricle of the heart via the pulmonary arteries to the lungs. There, the blood picks up O2 from inspiration and releases CO2 for expiration. This Oxygenated blood travels back to the left atrium of the heart and enters via the pulmonary veins

• Systemic Circulation:

  • Circuit through which oxygenated blood travels from the left ventricle of the heart via the aorta through the organ system. There, the blood delivers O2 from inspiration and picks up CO2 for expiration. This partially oxygenated blood travels back to the right superior vena cava and inferior vena cava

Heart Valves

Atrioventricular (AV) valves are between atria and ventricles:

• Tricuspid valve (3 flaps): 

  • between right atrium and right ventricle

• Bicuspid (mitrial) valve (2 flaps): 

  • Between left atrium and left ventricle

• Valve opens and closes due to pressure difference across it

  • Pressure can push a valve open or force it closed

• Papillary muscles

  • Limit valve movement to prevent backflow of blood into atria

Semilunar valves;

• Pulmonary valve;

  • Between right ventricle and pulmonary trunk (right and left pulmonary arteries)

• Aortic valve:

  • Between left ventricle and aorta

Cardiac Cycle: Diastole & Systole

Alternating contractions and relaxation of atria and ventricles (appx 0.8s)

• Systole

  • Period of ventricular contraction and blood ejection, appx 0.3s

• Diastole

  • Period of ventricular relaxation and blood filling, appx 0.5s

• Pressure

  • Forces exerted by blood (due to heart contraction)(mm Hg)

• Blood flow

  • Is from region of higher pressure to region on lower pressure (volume/unit time such as L/min)

Heart Sounds

• Two heart sounds heard through stethoscope

• First Sound: soft, low-pitch “lub”

  • Av valve closure, at onset of systole

• Second Sound: louder “dub”

  • SL valve closure, at onset of diastole

Cardiac Cycle: Diastole & Systole 

Systole:

1. Involumertic contraction: pressure in ventricles increases as ventricles begin contraction, causing AV valve to close (“lub”)

2. Ejection of blood into aorta and pulmonary trunk occurs when ventricular pressure (120 mm Hg, systolic blood pressure) exceeds aortic pressure so that semilunar valves open,

   1. Amount of blood ejected is the stroke volume; around ⅔ of the blood in the ventricles 

Diastole

3. Isovolumetric relaxation: Pressure in ventricles decreases, causing semilunar valves to close (“dub”). Aortic pressure is 80 mm Hgg (diastolic blood pressure).

4. When pressure in ventricles falls below atrial pressure, AV valves open and there is rapid filling of the ventricles (blood in atria _> ventricles).

5. Atrial contraction delivers final amount of blood into ventricles just prior to #1 occurring again.

   1. Volume of blood in ventricles at end of diastole is the end-diastolic volume (EDV)

Cardiac Cycle: Wiggers Diagram 

• Pressure and volume changes in the left ventricle during cardiac cycle 

  • Similar changes occur in the right ventricle, but the pressure is lower

• The cardiac cycle can be followed by measuring systolic and diastolic arterial blood pressures or by using an electrocardiogram (ECG)

Electrical Activity of the Heart

• Depolarization in sinoatrial (SA) node initiates Apps that spread to the rest of the cardiac cells, leading to contraction 

  • Small group of cardiac muscle cells in right atrium of heart

  • Heart pacemakers

  • Cells depolarize spontaneously and quick 

  • Excitation causes contraction

  • Aps spread through cells of atria via gap junctions, electrical synapses

• Atrioventricular (AV) node carries APs from right atrium 

• AP travels to ventricles via a bundle of His.

  • Slow conduction in AV node, so ventricular contraction occurs after atrial contraction has ended

Electrocardiogram (ECG, EKG)

• Detects electrical activity in the heart via electrodes on the surface of the skin 

• Electrodes record current conducted thorough fluid around heart, caused by simultaneous APs in myocardial cells

• There are three distinct ECG waves, P, Qrs, and T. 

  • P wave results from the spread of atrial depolarization 

  • QRS wave results from spread of depolarization into the ventricles

  • T wave results from repolarization of the ventricles

ECC & APs

• The relationship between the electrocardiogram (ECG or EKG), recorded as the difference between currants at the left and right wrist (left) and a action potential of typical ventricular myocardial cell (right)

Structure of Blood Vessels 

• Connective tissue, smooth muscle, and epithelial tissue (capillaries have only epithelial)

• Distribute blood to tissues, regulate blood pressure

• Closed loop: blood pumped from the heart in arteries return to the heart in veins

• Arteries branch into arterioles, vessels between arteries and capillaries

• In capillaries (smallest blood vessels) there is exchange of substances between cells and vessels, such as nutrients and waste

• Capillaries merge to form venules, vessels between capillaries and veins

• Venules merge into veins 

Blood vessels

• Arteries have strong, thick, elastic walls that resist flow

  • High Pressure/Low Volume

• Veins have weaker valves and wider lumen and fill easily 

  • Low Pressure/High Volume 

  • Act as volume reservoirs (54% of total volume)

Arterioles 

• The greatest pressure drop is in the arterioles 

• These vessels serve as controllers of flow into capillary beds

  • Vasoconstriction of arterioles (contraction of their smooth muscle layer to decrease diameter) decreases blood flow

  • Vasodilation of arterioles (relaxation of smooth muscle layer to increase diameter) increases blood flow 

Capillaries

Smallest blood vessels, mediate exchanges of substances with ISF

• In every tissue except cornea 

• Single layer of epithelium allows rapid exchange of substances 

  • Gas exchange (O2, CO2)

  • Nutrient and waste exchange 

  • Cell secretions

Veins

• Greatest total blood volume can expand with greater blood volume 

• Low pressure, but blood lows back to the heart due to the Skeletal muscle pump (skeletal muscle contraction), and the direction of flow is one-way due to venous valves in peripheral veins 

• Venous flow is assisted by the Skeletal muscle pump mechanism working in combination with one-way venous valves

• When muscle contracts, veins are partially compressed 

  • Diameter reduction, venous pressure increase, & increased volume of blood returning to the heart

Coronary Artery Disease and Atherosclerosis

• Coronary artery disease:

  • Insufficient blood flow (ischemia) to heart due to change in coronary arteries (arteries that nourish heart)

    • Can cause heart attack (Myocardial infarction)

• Primary cause is atherosclerosis in coronary arteries:

  •  thickening of arterial wall with plaques that include cholesterol and fat deposits

• Risk Factor: 

  • Hypertension, stress, smoking, obesity, sedentary lifestyle, diabetes, high cholesterol

Lymphatic System 

• Transport excess ISF that filtered out of blood vessels back to the blood 

• Transports fat absorbed from the small intestine into the blood 

• It's lymphocytes defend against disease-causing agents

• The lymph nodes filter lymph to remove pathogens before the fluid is retired to the blood

Ch 14 

Cardiac Output, Blood Flow, and Blood Pressure

Cardiac Output 

• Volume of blood pumped each minute by each ventricle 

  • Cardiac Output = Stroke Volume x Heart Rate

    • HR: Heart rate or cardiac rate (CR), beart/min

    • SV: stroke volume = volume of blood ejected per beat by each ventricle 

  • HR averages 70 beats/min and SV is 70-80 mL per beat (o.o7-0.08 L/beat)

    • CO averages 5500 mL/min or 5.5 L/min

  • CO is adjusted as needed, and is regulated by several factors

Regulation of Heart Rate 

• Sinoatrial (SA) node is rhythmically excited at appx. 100 beats/min (pacemaker potential)

  • HR is lower, at 70-75 beats/min, due to ACh release in parasympathetic nervous system 

    • ACh binds to muscarinic ACh receptors in cells of Sa nodes, resulting in slower rate depolarization 

• During fight or flight, NE in sympathetic nervous system and E from adrenal medulla bind to beta-adrenergic receptors in cells of SA node, resulting in faster rate of depolarization and increased HR

  • Other effects are increased contractility (strength of contraction) and faster contraction and relaxation 

Regulation of Stroke Volume 

1. End-diastolic Volume (EDV):

   1. Volume of blood in ventricles at end of diastole

   2. Greater EDV means Greater SV due to greater stretch of cardiac muscle

      1. Frank-Starling law of the heart (length-tension relationship for cardiac muscle)

2. Total Peripheral Resistance (TPR)

   1. Impedance to blood flow in the arteries

   2. Vasoconstriction is main cause of increased resistance

   3. Greater TPR means Lower SV

      1. Heart must work harder to eject blood due to resistance

3. Contractility 

   1. Strength of ventricular contraction 

   2. E and NE increase contractility meaning Greater SV

Frank-Starling Law of the Heart

• Stroke increases as EDV increases

  • Increasing the amount of stretch of cardiac muscle results in greater tension due to greater interaction between actin and myosin and increased release of Ca++ from SR

• To increase the stroke volume:

  • Fill the heart with more full blood (EDV). The increased stretch in the ventricle will align its actin and myosin in a more optimal pattern to overlap 

  • Deliver sympathetic signals (NE, E) to increase ventricular contractility. The heart will also relax more rapidly, allowing more time to refill.

Factors that Affect Cardiac Output 

• To Increase SV:

  •  increase EDV and sympathetic signals (NE, E) and decrease TPR

• To increase HR (cardiac rate):

  • Increase sympathetic signals (NE, E) (and reduce parasympathetic)

Blood Volume 

• Extracellular fluid, representing about ⅓ of the total body water, is distributed between ISF (80%) and blood (20%).

• Water is gained via drinking. Water is lost via excretion of urine, exhalation of air, sweating, and feces

• Within the body water is exchanged between the intracellular and extracellular compartments (ISF + blood plasma)

• Filtration 

  • Movement of fluid and solutes out the blood

• Absorption

  • Movement of fluid and solutes into the blood

• There are opposing forces, called Starling forces, constantly acting on walls of capillaries:

  • Blood pressure causes fluid and solutes to filter out the vessels to form ISF (filtration)

  • Osmotic forces cause water to be absorbed from tissues into the vessels (Absorption)

• Blood volume is regulated by mechanisms that affect drinking, urine volume, and distribution of fluid between plasma and ISF

  • Water loss and gain must be balanced (homeostasis).

• Kidneys also regulate blood volume

  • Urine is delivered from blood plasma

  • ADH (hypothalamus/posterior pituitary) and Aldosterone (adrenal cortex) act on kidneys to regulate blood volume by increasing or decreasing urine volume 

• There is also ANP (atrial natriuretic peptide), a hormone synthesized in atria of heart

  • Causes natriuresis 

    • Excretion of sodium in urine

    • When there is increased blood volume, the atria stretch, stimulating secretion of ANP

    • ANP secretion results in increased excretion of fluid and Na+ in the urine, in order to reduce blood volume 

Blood Flow 

• Blood flows from higher pressure region to lower pressure region 

• Blood flow is determined by the pressure difference between the mean pressure of 100 mmHg at origin of flow and the pressure at the end of the circuit (0mmHg) The mean pressure here is ~100mmHg

Blood Flow and CO during Exercise

• During moderate, sustained exercise, CO significantly increases from its baseline of appx 5.5 L/min

  • Ex: can reach 35 L/min in trained athletes

• Greatly increased flow to skeletal muscle, due to increased local metabolism, which results in vasodilation (also in cardiac muscle and skin)

• Vasoconstriction in GI system and kidneys due to sympathetic activity 

Blood Pressure 

• Blood pressure is affected by blood volume, TPR, heart rate, and stroke volume.

• Reduced diameter in arterioles increases resistance, to reduce “downstream” blood flow and pressure

• Increased SV, HR, and CO can increase blood pressure

• Kidneys regulate blood volume (and stroke volume) to regulated blood pressure

• Baroreceptor reflex maintains blood pressure

Vasicinstruoin and Blood Pressure 

• Constriction (arterioles_) increases pressure upstream (arteries) and decreases it downstream (capillaries, veins)

Blood Pressure and Baroreceptors

• Baroreceptors are stretch receptors in the heart whose action potential frequency is directly proportional to M.A.P.

Mean Arterial Pressure (M.A.P)

• Average pressure during cardiac cycle (appx 100mmHg)

• Sufficient blood flow to tissues is critical to health & survival so maintaining MAP is critical 

  • MAP =CO x TPR

  • MAP = DP = (⅓ x pulse pressure)

    • Where pulse pressure = systolic - diastolic

• Arteriolar resistance changes with vasodilation or vasoconstriction, and is typically the cause of a change in TPR, regulating MAP

Clinical Situation: Hypotension 

• Low blood pressure

  • Reduces blood flow to the brain and cardiac muscle

  • Response is baroreceptor reflex

    • Causes include:

      • CV disease, defect, or event, (e.g. valve disease, obstruction, heart attack)

      • Dehydration, diarrhea, vomiting, large uring loss, severe sweating, burns, hemorrhage

      • Neural, endocrine defects

      • Medication

Arterial Baroreceptor Reflex

• Baroreceptors deliver information about MAP to the medulla oblongata of the brain (controls heart, lungs). The result is autonomic output to heart and vessels 

Clinical Situation Hypertension 

Chronic high blood pressure, above 140/90 mmHg

• Excessively high pressure can cause damage to blood vessels leading to stroke

• Left ventricle must pump against increased arterial pressure, so left ventricular hypertrophy occurs,eventually leading to heart failure

  • Causes include:

    • Unknown (could be genetic, environmental/diet) (primary or essential  hypertension)

    • Atherosclerosis of aorta (secondary hypertension)

    • Kidney disease leads to decreased urine formation (secondary hypertension)

    • Endocrine disorders (secondary hypertension)

• Treatments for hypertension include smoking cessation, lowered alcohol intake, lowered sodium intake, increased potassium intake, increased exercise, weight reduction, and medication 

Blood Pressure classification in adults 

• Normal 

  • Under 120 mmHG Systolic blood pressure

  • Under 80 mmHG Diastolic blood pressure

• Elevated 

  • 120-129 mmHG Systolic blood pressure

  • Less than 80 mmHG Diastolic blood pressure

• Stage 1 Hypertension 

  • 130-139 mmHG Systolic blood pressure

  • 80-89 mmHG Diastolic blood pressure

• Stage 2 Hypertension 

  • 140 mmHg or greater Systolic blood pressure

  • 90 mmHG or greaterDiastolic blood pressure

Clinical Situations: Congestive Heart Failure

When CO is insufficient for maintain adequate blood flow

• Leads to increased fluid retention, which results in increased blood flow volume, increase stroke volume, increased EDV, hypertrophy, and more

• The failing heart is less able to change large EDV

  • Causes include:

    • Heart attack (myocardial infarction, often due to atherosclerosis)

    • Hypertension

    • Incompetence of heart valves

    • Electrolyte imbalance

  • Treatments:

    • Diuretics,  medication increase contractility, vasodilators, and medications that affect renal hormones like aldosterone

Ch 16 

Respiratory Physiology 

Respiratory System 

• Oral and nasal cavities, lungs, tubes that lead to lungs, and chest structures that move air into and out of lungs during breathing 

• Intakes O2 that diffuses into the blood for delivery to body tissues

• Eliminates CO2 (end product of cell respiration) from the blood

Respiration 

Three types:

• Ventilation: mechanical process that moves air into and out of the lungs

• Gas Exchange: Exchange of gases between the air and blood vessels in the lungs and between blood and other tissues of the body. Occurs by diffusion.

• Oxygen Utilization: Use of oxygen in cell respiration 

Zones

Start to finish

1. Nose/Mouth 

2. Pharynx

3. Larynx

4. Trachea

5. Bronchus

6. Lung 

 In the lungs 

1. Left and right primary bronchi 

2. Bronchioles

3. Terminal bronchioles

4. Respiratory bronchioles (some alveoli attached) 

5. Alveolar ducts

6. Alveolar sacs

7. Alveoli

Upper airways:

• Nose/Mouth, pharynx, larynx (voice box)

Conducting zone:

• All structures through which air passes before reaching the respiratory zone, i.e. mouth to terminal bronchioles

  • Conducts air to the respiratory zone

  • Warms and humidifies inspires air 

  • Filters and cleans air

Respiratory zone:

• Region where gas exchange occurs, compressing the respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli 

• Most gas exchange occur in the ~ 8mil alveolar sacs

Trachea and bronchi have rings of cartilage. Bronchioles are surrounded by smooth muscles, not cartilage. The relaxation/contraction of circular smooth muscle lining these “airways” determines how easily airflow can occur ( bronchodilation vs. bronchoconstriction)

Cross-Section of Thoracic Cavity 

• The intrapleural space (or pleural cavity) between the parietal and visceral pleura (epithelial membranes) contains a thin layer of fluid which acts as a lubricant

Protective Mechanism

1. Nasal hairs and muscle trap particles

2. Mucus escalator keep lungs clear

   1. Ciliated cells in airways carry mucus and particulate matter into the pharynx to be swallowed 

3. Bronchoconstriction: response to irritation, prevents particulate matter from entering alveoli 

4. Macrophages: WBCs in airways and alveoli engulf/destroy inhaled particles and bacteria

Ventilation & Lung Mechanics

• Air passively moves from high pressure region to low pressure region, determined by intra-alveolar and atmospheric pressures

  • Intra-alveolar Pressure = Palv = pressure inside lungs

  • Atmospheric Pressure = Patm = 760 mmHG at sea level

    • If Palv <  Patm inspiration occur (air moves into lungs where pressure is lower)

      • Hint*  on a mountain

    • If Palv >  Patm expiration occurs (air moves out of lungs)

      • Hint* Underwater

• Air passively moves into and out of the lungs because Palv alternates between being lower than Patm and greater than Patm

  • Pressure is inversely proportional to the volume (V), so volume of the lungs determines pressure in lungs: Boyle’s law: P!V1= P2V2

  • Increased lung volume reduced pressure of inside lungs resulting in inspiration

  • Decreased lung volume increases pressure inside of lungs resulting in expiration

Inspiration 

Movement of air from external environment through airways into alveoli during breathing: inhalation

• Results from contraction of the diaphragm 

  • Downward contraction expands thoracic cavity to increase thoracic volume and lung volume, passive enlargement of lungs

  • Results in decreased Pressure inside of lungs which causes air to move into the lungs 

    • Palv <  Patm

• Contraction of parasternal and external intercostal muscles in chest wall raises the ribs and increases thoracic volume as well

Expiration 

Movement of air from the alveoli to the external environment during breathing: exhalation 

• Muscle relaxation causes chest wall and lungs to recoil inward due to elasticity 

• Reduced lung volume increases pressure inside of lungs, so air moves out of the alveoli into the atmosphere

  • Palv >  Patm

• Diaphragm relaxes and is raised, and lung volume decreases, increasing Pressure inside of lungs

Muscle of Breathing 

Expiration:

• Relaxation of inspiration muscles to reduce thoracic volume and increase Palv

Inspiration 

• Contraction of diaphragm, parasternal & external intercostals to increase thoracic volume and reduce Palv

Lung Volumes & Capacities

Lung volume is measured using Pulmonary Function Test 

• The tidal volume is them out of air moved in (or out) of the airways in a single breath cycle (500 mL)

• Inspiratory (3000 mL) and expiratory (120 mL) reserve volumes are, respectively, the additional volume that can be inspired or expired.

• All three quantities sum to the lungs vital capacity (4700 mL)

• The residual volume is the amount of air that must remain in the lungs to prevent alveolar collapse (1200 mL)

Alveoli

• The airways end in clusters of epithelium-lined air sacs called alveoli (plural form of alveolus)

• These thin-walled structures function as gas exchange surfaces

• There are around 300 million alveoli, providing a large surface area for gas diffusion 

• Type 1 alveolar cells

  • Form most of the epithelium

• Type 2 alveolar cells

  • Secrete a detergent-like substance called surfactant

    • Decreases surface tension in alveoli to prevent alveolar collapse

• Macrophages

  • Also present

Alveoli and Blood Vessels

• Each of the clustered alveoli includes an abundance of pulmonary capillaries, thereby ensuring that the ventilated air is brought into close proximity to the blood, allowing efficient and through gas exchange between the air and the blood 

Gas Exchange in Alveoli & tissues

• Diffusion of gas in liquid follows a pressure gradient (high pressure region to low pressure region) 

• The pressure of each individual gas is its partial pressure and is proportional to its concentration

• Oxygen from alveoli diffuses into capillaries, transported to tissues, enters ISF, enters cells

• Carbon dioxide from cells diffuses into ISF, then capillaries, then transported via bloodstream to alveoli 

Partial Pressures of Gases

• Changes in the pressures or concentration of dissolved gases are indicated as the blood circulates in the body 

• In the lungs, the concentration gradient favors the inward (toward the blood) diffusion of oxygen and the outward (towards the alveolar air) diffusion of carbon dioxide

• Due to the metabolic activities of cells, these gradients are reversed at the interface of blood and the active cells

Control of Respiration 

• Nerual 

  • Motor neurons cyclically stimulate skeletal muscle contraction and relaxation

• Chemical: Blood pH and Gas Content 

  • Peripheral chemoreceptors in heart & carotid arteries 

  • Central chemoreceptors in medulla oblongata of brain 

  • Detect changes in PO2, PCO2, [H+]  to keep them daily constant. Ventilation rate is regulated

CO2 Chemistry 

CO2 + H2O <->H2CO3 <->H++HCO3-

• Reversible reaction 

• Increased [CO2] left to right 

• INcreased [H+] right to left

• Controlling [CO2] means controlling pH

• Bicarbonate serves as a buffer for H+

Effects of Blood [CO2] on Ventilation 

• Hypoventilation in inadequate ventilation

• During hypoventilation, PCO2 increases

  • Reaction proceeds to the right, and pH decreases (due to increased H+ when carbonic acid releases H+)

  • This triggers an increase ventilation 

• Hyperventilation is increased ventilation

• During hyperventilation, PCO2 decreases

  • Reaction proceeds to the left and pH increases (due to excessive elimination of carbonic acid)

  • This triggers a decrease in ventilation rate

Chemical Control of Respiration 

• Chemoreceptors that respond to increased carbon dioxide level in the blood and resulting decreased pH “inform” the respiratory center in the medulla oblongata of the brain to increase the rate of ventilation 

• Acidosis: pH below 7.35

• Alkalosis: pH above 7.45

O2 Transported in Blood 

• Blood carries around 20 mL of oxygen per 100 ml of blood 

  • 1.5% is dissolved as a gas in plasma and RbCs

  • 98.5% is bound to hemoglobin in RBCs

  • Blood oxygen-carrying capacity is determined its hemoglobin concentration

• Hemoglobin molecule: 4 globins (polypeptides) bound to 4 hermes (pigment molecules)

  • In center of heme, there is one atom of iron (Fe2+) that can combine with one O2 molecule, so each hemoglobin molecule can combine with 4 oxygen molecules

  • Oxyhemoglobin:  hemoglobin with oxygen 

  • Deoxyhemoglobin: hemoglobin from which oxygen has dissociated to release O2 to the tissues 

  • Loading of O2 occurs in pulmonary capillaries and unloading occurs in systemic capillaries

CO2 transport in Blood 

• 10% dissolved as a gas in plasma and RBCs

• 20% as carbaminohemoglobin, i.e. bound to deoxyhemoglobin 

• 70% is transported as HCO3 (bicarbonate)

Ventilation During exercise

• During light to moderate exercise, ventilation increases to keep up with increased metabolism, so PO2, PCO2, and pH remains relatively constant.

• Breathing becomes deeper and faster

• There is increased O2 delivery to skeletal muscles

During heavy exercise, PCO2 decreases and pH increases