The lymphatic system returns fluids leaked from

blood vessels back to blood

- consists of 3 parts:

1) Network of lymphatic vessels (lymphatics)

2) Lymph: fluid in vessels

3) Lymph Nodes: cleanse lymph

Lymphoid organs + tissues provide structural basis of immune system by housing

phagocytic cells + lymphocytes

- Structures include: spleen, thymus, tonsils, lymph nodes, + other lymphoid tissues

Network of lymphatic vessels (lymphatics)

- elaborate network of drainage vessels

- circulates ~ 31 interstitial fluid per day

- once interstitial fluid enters lymphatics, it is called lymps

Lymphatic vessels offer a one-way system, ensuring lymph flows only toward

heart

Lymph vessels (lymphatics) include lymphatic capillaries + larger lymphatic vessels

Lymphatic capillaries: blind-ended vessels that weave between tissue cells + blood

capillaries

- more permeable than blood capillaries

↳ can take up larger molecules + particles that blood capillaries cannot

(proteins, cell debris, pathogens, + cancer cells)

- can act as route for pathogens or cancer cells to travel throughout the body

↑ permeability due to 2 structures:

1) endothelial cells overlap loosely to form one-way minivalves

2) minivalves are anchored by collagen filaments to matrix, so increases in ECF volume open minivalves

even more

- decreases in ECF cause minivalves to close

Lacteals: specialized lymph capillaries present in intestinal mucosa

- absorb digested fat + deliver fatty lymph (chyle) to the blood

Larger Lymphatic vessels:

- lymph capillaries drain into increasingly larger vessels called collecting lymphatic vessels

- consists of collecting vessels, trunks, + ducts

- have structures similar to veins except: have thinner walls, + more internal values.

Anastomose more frequently

- collecting vessels in skin travel with superficial veins, but deep vessels travel with arteries

Lymphatic trunks (formed by union of largest collecting vessels) drain large areas of the body

- named for regions of body they drain (paired lumbar, paired subclavian, etc)

Lymph is delivered from trunks into 1 of 2 large lymphatic ducts

- Right lymphatic duct drains right upper arm + right side of head + thorax

- Thoracic duct drains rest of body

- starts out as an enlarged sac, cisterna chyli

Each duct empties lymph into venous circulation @ junction of internal jugular + subclavian veins on its own

side of body

Lymphangitis: condition in which lymphatic vessels appear as painful red lines under the skin

- caused by inflammation of larger lymphatic vessels that contain vaso vasorum

vaso vasorum become congested with blood

- larger lymphatics (blood vessels) receive their nutrients from branching vaso vasorum

Lymphoid tissue

functions:

- houses + provides proliferation sites for lymphocytes

- offers surveillance vantage points for lymphocytes + macrophages as they filter thru lymph

composed mostly of reticular connective tissue

- macrophages live on reticular fibers

- spaces between fibers offer a place for lymphocytes to occupy when they return from patroling

body

2 main types:

Diffuse lymphoid tissue: loose arrangement of lymphoid cells + some reticular fibers

- found in almost every organ

Lymphoid follicles (nodules): solid, spherical bodies consisting of tightly packed lymphoid cells + reticular

fibers

- contain germinal centers of proliferating B cells

- may form part of larger lymphoid organs (nodes)

Lymphoid organs:

2 functional categories:

- primary lymphoid organs: areas where T + B cells mature (red bone marrow + thymus)

- T + B cells originate in red bone marrow, but only B cells mature there;

T cells mature in thymus

- secondary lymphoid organs: areas where mature lymphocytes first encounter their antigen + become activated

(nodes, spleen, MALT, + diffuse lymphoid tissues)

Lymph Nodes: principal secondary lymphoid organs of body

- most deep in connective tissue along lymphatic vessels

2 main functions:

1) Cleansing the lymph: act as lymph "filters"

- macrophages remove + destroy microorganisms + debris that enter lymph

- prevent unwanted substances from being delivered to blood

2) immune system activation: offer a place for lymphocytes to become activated + mount an attack against antigens

2 regions of node: cortex + medulla

cortex: has germinal centers that are heavy with dividing B cells (multiplying)

- deep cortex houses T cells in transit

T cells circulate continuosly among blood, lymph nodes, + lymph

- abundant #of dendritic cells are closely associated w/ both Tt B cells

Play a role in activating both lymphocytes

Medulla: medullary cords extend inward from cortex + contain B cells, T cells, + plasma cells

Lymph sinuses: found throughout node

- consist of large lymphatic capillaries spanned by crisscrossing reticular fibers

macrophages reside on fibers, checking for + phagocytizing any foreign matter

Lymph enters convex side of node via afferent lymphatic vessels, travels thru large sub capsular sinus +

then into smaller sinuses, finally exits concave side @ hilum via efferent lymphatic vessels

Spleen: site of lymphocyte proliferation + immune surveillance + response

- cleanses blood of aged blood cells + platelets; macrophages remove debris

- stores breakdown products of RBCs for later reuse

- stores blood platelets + monocytes for release into blood when needed

- May be site of fetal erythrocyte production

2 components: white + red pulp

White pump: where immune function occurs

red pump: site where old blood cells + blood borne pathogens are destroyed

Mucosa-associated lymphoid tissue (MALT)

- lymphoid tissues in mucosa membranes throughout body

- protects from pathogens trying to enter the body

- found in tonsils, peyer's patches, + appendix

Tonsils: gather + remove pathogens in food or air

Peyer's patches: destroy bacteria, preventing them from breaching intestinal wall

- generate "memory" lymphocytes

appendix: same functions as Peyer's patches

Thymus: lymphoid organ where T cells mature

- thymic corpuscle's are where regulatory T cells develop

Regulatory T cells: type of T cell that helps to prevent auto immunity

Lymph system is a low pressure system like the venous system

Lymph is propelled by the same mechanisms:

- milking action of skeletal muscle

- pressure changes in thorax during breathing

- values to prevent backflow

- pulsations of nearby arteries

- contractions of smooth muscle in walls of lymphatics

Physical activity increases flow of lymph; immobilization of area keeps needed inflammatory

material in area for faster healing

Lymphedema: severe localized edema

- caused by anything that prevents normal return of lymph to blood

(tumors blocking lymphatics/removal of lymphatics during cancer surgery)

•

Lymphoid cells consist of:

1) immune system cells found in lymphoid tissue

2) supporting cells that form lymphoid tissue structures

1) Immune system cells:

Lymphocytes: cells of the adaptive immune system; mature into one of two main

types:

T cells: manage immune response + some attack + destroy infected cells

B cells: produce plasma cells, which secrete antibodies

- antibodies mark antigens for destruction by phagocytosis or other means

Both protect against antigens (anything body perceives as foreign-bacteria, toxins, cancer, etc)

Other lymphoid immune cells:

- macrophages phagocytize foreign substances + help activate T cells

- dendritic cells capture antigens + deliver them to lymph nodes; also help activate T cells

Supporting lymphoid cell:

- Reticular cells produce reticular fibers called stroma in lymphoid organs

Stroma: network-like support that acts as scaffholding for immune cells

- antibodies mark antigens for destruction by phagocytosis or other means

- also called immunoglobulins

- proteins secreted by plasma cells

Antibody classes:

1g D: monomer attached to surface of B cells

functions as B cell receptor

IgG: monomer, 75-85% of antibodies in plasma

crosses Placenta barrier

IgE: monomer active in some allergies + parasitic infections

causes mast cells and basophils to release histamine

IgM: first antibody released

potent agglutinating agent. readily fixes + activates compliment

IgA: monomer or dimer

helps prevent entry of pathogen

Antibodies do not destroy antigens, they inactivate + tag them

- form antigen-antibody (immune) complexes

defensive mechanisms by antibodies:

- neutralization: antibodies block specific sites on viruses or bacterial exotoxin

- prevents antigens from binding to receptors on tissue cells

Agglutination: antibodies can bind same determinant on 2 different antigens@ the same time

- each antibody has 2 arms, each containing a variable region capable of binding to one

antigen

- allows for antigen-antibody complexes to become cross-linked into large lattice-live clumps

Precipitation: soluble molecules are cross-linked into complexes

precipitated are easier for phagocytes to engulf

Complement fixation + activation: main antibody defense against cellular antigens

when several antibodies are close together on the same antigen, complement-

binding sites on their stem regions are aligned

- alignment triggers complement fixation, which leads to cell lysis

monoclonal antibodies: commercially prepared pure antibodies that are specific for a single

antigenic determinant

produced by hybrid omas, cell hybrids formed from fusion of tumor cell + B cell

Tumor cell portion allows cell to proliferate

B cell portion allows production of single type of antibody

active immunity: occurs when B cells encounter antigens and produce specific antibodies against them

2 types:

naturally acquired: formed in response to actual bacteria or viral infection

artificially acquired: formed in response to vaccine of dead or attenuated pathogens

Passive immunity: occurs when ready-made antibodies are introduced into body

- B cells are not challenged by antigens; immunological memory does not occur

2 types:

Naturally acquired: antibodies delivered to fetus via placenta or to infant through milk

artificially acquired: injection of serum, such as gamma globulin

Protection immediate but ends when antibodies degrade in body

-

Innate system uses the first and/or second lines of defense to stop attacks by pathogens (dig:{frigging

first line of defense: surface barriers

- Skin + mucous membranes + their secretions

• Physical barrier to most microorganisms

Skin + mucous membranes produce protective chemicals that inhibit or destroy microorganisms

Acid: acidity of skin + some mucous secretions inhibits growth; called acid mantle

Enzymes: lysozyme of saliva, respiratory mucus, + lacrimal fluid kills many microorganisms,

enzymes in stomach kill microorganisms

Mucin: sticky mucus that lines digestive + respiratory tract traps microorganisms

Defensins: antimicrobial peptides that inhibit microbial growth

Other chemicals: lipids in sebum + dermoidin in sweat are toxic to some bacteria

Respiratory system has modifications to stop pathogens

- mucus-coated hairs in nose trap inhaled particles

- cilia of upper respiratory tract sweep dust-and-bacteria-laden mucus toward mouth

Second line of defense: Cells + Chemicals

refers to the innate immune system, which acts when pathogens bypass the first line of

defense (skin/mucous membranes) + penetrate deeper into body

- nonspecific: responds to broad range of pathogens without prior exposure

Phagocytes: immune cells like macrophages + neutrophils that engulf foreign invaders

through phagocytosis

Natural Killer Cells (NK (s): attack + destroy cells infected w/ virus/become cancerous,

without prior sensitization

Inflammatory response: body's localized response to injury or infection.

involves:

macrophages + mast cells: release chemicals to recruit other immune cells to site

White blood cells (WB (s): like neutrophils + monocytes that respond to infection

Inflammatory chemicals: (histamines), increase blood flow + permeability of blood vessels

to allow immune cells to reach infection site

Antimicrobial proteins:

interferons: proteins released by virus-infected cells to help protect nearby

unaffected cells

complement proteins: mark pathogens for destruction + insist in killing directly by

forming holes in membrane

Fever: ↑ body temp, enhances immune response by speeding up the metabolism

Of immune cells + hindering replication of pathogens

Pattern recognition receptors: can detect common molecular structures found on pathogens, bind tightly to

structures on microbes, and initiate an immune response (disarming them

before they do harm)

Toll-like receptors: plays a critical role in detecting + responding to pathogens. They bind to microbes,

which triggers signaling pathways that activate immune response

Friend! ptamges.tt?nderthn tissue spaces (ex: alveolar macrophages)

Fixed macrophages: permanent residents of some organs (ex: stellate macrophages-liver or microglia-brain)

3rd line of defense: Adaptive defenses:

Adaptive immune system is a specific defense system that eliminates almost any pathogen or abnormal cell in body

activities:

- amplifies inflammatory response

- activates complement

Shortcoming: must be primed local exposure to specific foreign substance

- priming takes time

Characteristics:

- specific: recognizes + targets specific antigens

- systemic: not restricted to initial site

- memory: mounts stronger attack to "known" antigens

2 branches:

- Humoral (antibody-mediated) immunity: antibodies, produced by lymphocytes, circulate

freely in body fluids

- nd temporarily to target cell, temporarily inactivate, mark for destruction by phagocytes or complement

has extracellular targets

- Cellular (cell-mediated) immunity: lymphocytes act against target cell

• Directly: by killing infected cells

- Indirectly: by releasing chemicals that enhance inflammatory response; or

activating other lymphocytes or macrophages

- has cellular targets

- recognizes foreign material primarily by distinguishing between self + non-self. Important because

it makes sure we identify + attack pathogens while avoiding damage to the body's own cells.

Pattern Recognition Receptors (PRRS):

- identifies pathogen-associated molecular patterns (PAMPS) + damage-associated molecular patterns (DAMPS)

PAMPs: found on surface of many pathogens, not on human cells

DAMPS: molecules released by damaged or dying host cells, signaling need for immune action.

Examples of PRRs: Toll-like receptors + NOD-like receptors

Major Histocompatibility Complex (MHC) Molecules:

- the adaptive immune system uses MHC molecules to present fragments of foreign material to immune cells:

MHC class I: displayed by all cells except RBCs

- present short fragments of endogenous antigens derived from proteins in cell

Endogenous antigen can be:

self-antigen: normal proteins of cell

Nonself-antigen: abnormal proteins found in infected or abnormal cell

Critical for cell activation, inform cytotoxic T cells of microorganisms hiding in cells.

MHC class 2: bind with longer fragments of exogenous (extracellular) antigens that have been engulfed and broken down in a phago lysosome by antigen presenting cell

Recognized by helper T cells

Signal CD4 cells that help is required

Antigen Presentation

when pathogen enters body, antigen-presenting cells (APCs) like dendritic cells + macrophages engulf + digest it

They process the pathogen's proteins into smaller fragments (antigens) + these antigens are presented on MHC proteins to

T cells

Helper T cells: recognize antigens presented on MHC class 2 molecules + help activate other immune

cells (B cells + cytotoxic T cells)

Cyto toxic T cells: recognize antigens presented on MHC class I molecules + kill infected or abnormal cells

T cells can be activated only when antigen is presented to them

2 step process:

1) Antigen-binding: T cell receptors bind with antigen from APC

- recognizes foreign antigen + MHC protein

- triggers pathways to start T cell activation

2) Co-stimulation: bind to one or more costimulatory signals on APC to make T cell mature + respond

without co-stimulation, anergy occurs

become tolerant to antigen, unable to divide, + don't secrete cytokines

B cells + antibodies:

- the adaptive immune system uses Balls, which produce antibodies that specifically recognize + bind

to foreign antigens

Each B cell has receptors (B receptors) on surface that recognize a specific antigen

- when B cell encounters a foreign antigen that matches receptor, it can be activated (with help of helper T cells) to produce lots of antibodies

- antibodies bind to pathogen, marking for destruction by other immune cells or neutraling them directly

Self vs Non self recognition:

Self-recognition: immune system avoids attacking body's own cells due to processes like central tolerance (in thymus or

bone marrow) + peripheral tolerance (other tissues). These mechanisms ensure immune cells that react to body's own antigens

are eliminated/inactivated.

Non-self recognition: when immune cells encounter foreign molecules not found in body's own tissue, they

recognize them as non-self + initiate immune response

vaccines

- stimulate immune system to recognize + fight specific pathogens without causing disease

- introduce weakened, inactivated, or parts of pathogen (proteins) to trigger immune response

Purpose:

Prevent disease: prepares immune system to recognize + fight pathogens if exposed to later

develop immunity: helps body produce antibodies + memory cells for long-term protection

reduce disease severity: if infection occurs, symptoms may be milder in vaccinated individuals

Most blood vessel walls have 3 layers

Tunica Intima: innermost tunic

- in intimate contact with the blood in the lumen (blood-containing space)

- contains the endothelium, which lines the lumen of all vessels

- minimizes friction as blood moves through lumen

Tunica Media: the middle tunic

- mostly smooth muscle + sheets of elastin

- activity of smooth muscle is regulated by sympathetic vasomotor nerve fibers of ANS

- depending on needs, regulation may cause vasoconstriction or vasodilation.

- small changes in lumen diameter greatly influence blood flow + blood pressure.

- maintaining blood pressure + circulation

Tunica Externa: outermost layer of blood vessel wall

- mostly woven collagen fibers, which protect + reinforce the vessel, and anchor it to surrounding structures

Vasa vasorum: nourish the more external tissues of the blood vessel wall

vasoconstriction: lumen diameter decreases as the smooth muscle contracts

vasodilation: lumen diameter increases as the smooth muscle relaxes

Arteries are pressure reservoirs, distributing vessels, or resistance vessels

3 types of arteries: elastic, muscular, and arterioles

elastic arteries: thick walled arteries near the heart

- largest in diameter + most elastic

- large lumens make them low-resistance pathways that conduct blood from the heart to medium-sized arteries.

.-"conducting arteries"

relatively inactive in vasoconstriction.

- pressure reservoirs, expanding + recoiling as the heart ejects blood

↳ blood flows continuosly

muscular arteries:

- deliver blood to specific body organs

"distributing arteries"

- thickest tunica media (has more smooth muscle + less elastic tissue)

- active in vasoconstriction + less capable of stretching

arterioles: smallest of the arteries

- smaller arterioles lead into capillary beds

- blood flow into capillary beds is determined by arteriolar diameter, which varies in response to changing neural,

hormonal, + local chemical influences

- changing diameter changes resistance to blood flow

"resistance vessels"

- arterioles dilate = blood flow into capillaries increases dramatically

Capillaries are exchange vessels

- smallest blood vessels

- outer surface of some capillaries have pericytes (contractile stem cells that can generate new vessels or scar tissue, stabilize

the capillary wall, + help control capillary permeability)

- Tendons + ligaments are poorly vascularized (heal poorly). Cartilage + epithelia lack capillaries, but receive

nutrients from nearby blood vessels

- provide direct access to nearly every cell in the body.

- role: exchange of materials (gases, nutrients, hormones, + so on) between the blood + interstitial fluid

TYPES OF CAPILLARIES: continuous, fenestrated, + Sinusoid

continuous: least permeable + most common. blood brain barrier

- abundant in skin, muscles, lungs, + CNS

- often have pericytes

- intercellular clefts between endothelial cells

fenestrated: have large fenestrations (pores) that increase permeability

- occur in areas of active filtration (kidneys) or absorption (small intestine), + areas of endocrine

hormone secretion

sinusoid: larger openings between their cells (fenestrations) and looser connections (fewer tight junctions)

- larger lumens for blood to flow through

- incomplete basement Membranes

- blood flows slowly through them, which gives the body more time to modify or handle large molecules + blood cells moving between

the blood + surrounding tissues

- have macrophages that help catch + destroy foreign invaders

Capillary bed: a network of tiny blood vessels (capillaries) that connect arterioles to venules, allows

blood to flow between arterioles + venules

microcirculation: movement of blood through this capillary bed, starting from arteriole + ending in venule

terminal arteriole: small branch from arteriole that splits into about 10 to 20 capillaries (exchange vessels),

which makes up the capillary bed

- Capillaries are where important exchanges occur; oxygen + nutrients are delivered to surrounding

tissues, while waste products + carbon dioxide are picked up

- once exchange happens, blood is collected by the post-capillary venule, which carries

it back into the venuous system

Factors that control flow of blood

- flow of blood through a capillary bed is controlled by the diameter of the terminal

arteriole + upstream arterioles

- chemical signals from surrounding tissues + signals from nerve fibers that regulate

blood vessel constriction (called arteriolar vasomotor nerve fibers) control how

much blood enters capillary bed

When tissues need more blood (during exercise, etc), the arteriole + terminal arteriole widen

(dilate) to allow more blood to flow into capillary bed. If less blood needed, vessels constrict, reducing

blood flow + diverting it to other areas of body.

2 features that form a special arrangement of capillaries

1) Vascular shunt: direct pathway that connects the arteriole to the venule, allowing blood to

bypass the true capillaries

2) Pre capillary sphincter: regulate blood flow by acting as a valve. Controlled by local chemical signals

in tissue

- when the pre capillary sphincters are open, blood flows into the true capillaries for exchange.

when they are closed, blood is diverted through the vascular shunt, bypassing capillary bed.

Veins: begin @ post capillary venules + merge into larger veins

- carry blood towards heart

- venules converge to form small veins

- has all 3 tunics, thinner walls + larger lumen than arteries, tunica media is thin, tunica externa is thick

- lower pressure than arteries, makes adaptations to get blood to heart (contains values + large diameter lumens offer little resistance)

Capillaries unite to form Post-capillary venules: very porous to allow fluid + WBC into tissues

Capacitance vessels: what veins are called because they are good storage vessels due to large lumen

+ thin walls. They are blood reservoirs (contain 65% of blood supply)

why veins stretch

Venous valves: prevent backflow of blood

venous sinuses: flattened veins w/ very thin walls

varicose veins: dilated + painful veins due to leaky valves

Vascular anastomoses: interconnections of blood vessels

Arterial anastomoses: alternate pathways to ensure continuous flow, even if I artery is blocked

Arteriovenous anastomoses: shunts in capillaries

Venous anastomoses: so abundant that occluded veins rarely block blood flow

Blood flow

volume of blood flowing through vessel, organ, or entire circulation in a given period

- measured in mL/min

- equivalent to cardiac output for entire vascular system

Bloodpressure: force per unit area exerted on wall of blood vessel by blood

- MmHg is the unit

- pressure gradient keeps blood moving from higher to lower pressure areas

Resistance: opposition to flow

- Measurement of the amount of friction blood encounters with vessel walls

SOURCES OF RESISTANCE:

1) Blood viscosity

2) Total blood vessel length

3) blood vessel diameter

Blood viscosity: the thickness or "stickiness" of blood due to formed elements + plasma proteins

- greater the viscosity, the less easily molecules are able to slide past each other

↑ viscosity = ↑ resistance

TOTAL BLOOD VESSEL LENGTH: the longer the vessel, the greater the resistance encountered

BLOOD VESSEL DIAMETER: greatest influence on resistance

- frequent changes alter peripheral resistance .

↓ radius, ↑ resistance

Turbulent flow: irregular flow that causes increased resistance

If blood pressure gradient increases, blood flow speeds up

If peripheral resistance increases, blood flow decreases

- - -

Arteries: carry oxygen-rich blood away from heart to body

- thick, muscular, + elastic walls to withstand high pressure of blood pumped through heart

- narrow lumen: helps maintain high pressure for blood flow

Veins: carry oxygen-poor blood back to heart

- thin walls, less muscle + elasticity because pressure is lower

- larger lumen: to accoma date slower blood flow @ low pressure

- values: prevent backflow of blood, make sure it goes to heart

- thinner tunica media than arteries

Arteries:

Direction: away from heart

Pressure: high pressure (pumped directly by heart)

Flow: moves in strong surges in sync with heart beats

Assistance: the elastic muscular walls expand + contract with each heartbeat-helps blood propel forward

Oxygenation: carry oxygen-rich blood to tissues of body

Veins:

Direction: to the heart

Pressure: low pressure (traveled thru capillaries + loses initial force)

Flow: flows smoothly + steadily w/ no pulses. Slower due to ↓ pressure

Assistance:

Values: prevent back flow

Skeletal muscle contractions: when muscles contract, they compress veins, helps push blood to heart

Respiratory pump: breathing movements help create pressure changes in the chest cavity to assist blood back to heart

Oxygenation: carry oxygen-poor blood from tissues to heart

ARTERIAL BLOOD PRESSURE: determined by 2 factors

elasticity (compliance or distensibility) of arterioles close to heart

volume of blood forced into them at any time

blood pressure near heart is pulsatile rises + falls w/each heartbeat)

Short term regulation:

short term: neural + hormonal controls

Neural Controls:

Baroreceptor Reflex:

Baroreceptors in the carotid arteries + aorta sense changes in blood pressure

- If blood pressure rises, baroreceptors send signals to the brain (medulla) to:

- dilate blood vessels (vasodilation) to lower pressure

• Slow heart rate (reduced cardiac output) via parasympathetic nervous system

- If blood pressure lowers, they trigger:

- vasoconstriction (narrowing blood vessels) to raise pressure

• increase heart rate + stronger heart contractions via sympathetic nervous system

Chemoreceptor reflex: found in aortic arch + large arteries of neck

detects increase in CO2 levels

- decrease in PH

- drop in O2 levels

responds to:*:#fessure by:

cardio acceleratory center → increases cardiac output

- activating vasomotor center → increases vasoconstriction (narrows blood vessels, ↑ blood pressure)

Hormonal controls:

Epinephrine: regulate adrenal gland during stress/exercize, increases heart rate + vasoconstriction

(raise blood pressure)

Angiotensin 2: potent vasoconstricter, ↑ blood pressure

Anti diuretic hormone (ADH): ↑ levels can cause vasoconstriction

Long-term regulation

Long-term: renal controls

Renal controls:

- involves regulating blood volume, managed by kidneys + many hormones

Direct renal mechanism: alters blood pressure independently of hormones

- increased blood pressure or volume causes elimination of more urine = ↓ blood pressure

- decreased blood pressure or volume causes kidneys to conserve water = ↑ blood pressure

Indirect renal mechanism:

Renin-Angiotensin-Aldosterone System (RAAS):

- when blood pressure is low, kidneys release renin, leads to production of angiotensin II, the

hormone that:

- causes vasoconstriction to raise blood pressure

- stimulates release of aldosterone from adrenal glands, which causes

kidneys to retain sodium + water = ↑ blood pressure + volume