Name: liver detox and the urea cycle
Uploaded: 2025-10-23T11:49:08.000Z
Duration: 1 min 23 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Human Anatomy and Physiology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

9-12.HA.1.11

Urea Cycle

The urea cycle is the primary way that mammals eliminate ammonia, a nitrogenous waste product of protein catabolism, from the body through the conversion to urea, which is accomplished by cells in the liver.

Starting in the cellular mitochondria, ammonia is first changed to the compound carbamoyl phosphate, using bicarbonate, energy in the form of ATP, and the enzyme carbamoyl phosphate synthetase 1.

Next, the enzyme ornithine transcarbamylase combines carbamoyl phosphate and the amino acid ornithine into citruline which is transferred to the cytosol.

In this third step, citruline combines with aspartate to form arginosuccinate. This reaction is an enzymatic one governed by arginosuccinate synthetase, and requires a large amount of energy by converting ATP to AMP.

Arginosuccinate is then cleaved into arginine and fumarate by the enzyme arginosuccinate lyase.

In the final step, the enzyme arginase 1 splits arginine into urea and ornithine. Urea is ultimately excreted by the kidneys. Ornithine goes back to the mitochondria to participate in the urea cycle again.

urea cycle

The urea cycle describes how liver cells convert ammonia to urea. Ammonia is a toxic waste product of protein catabolism. Land animals must convert ammonia into the less toxic urea which can be safely eliminated by the kidneys through urine. Marine animals excrete ammonia directly, and the surrounding water dilutes the ammonia to safe levels.

There are five basic steps in the urea cycle:

<ol>
	<li>the conversion of ammonia (NH3) to carbamoyl phosphate</li>
	<li>the introduction of ornithine in the transformation of carbamoyl phosphate to citrulline</li>
	<li>the transformation of citrulline into arginosuccinate involving aspartate and chemical energy (ATP)</li>
	<li>the conversion of arginosuccinate into arginine with fumarate as a by-product</li>
	<li>the formation of urea and ornithine from arginine</li>
</ol>

Notice that ornithine is used in the second step and is regenerated in the last step. Since ornithine is recycled, the urea cycle is sometimes referred to as the ornithine cycle.

Elevated levels of blood ammonia, or hyperammonemia, results from an interruption of the urea cycle. This can occur at the organ level where scar tissue blocks the blood supply to the liver. Scar tissue, or cirrhosis, can result from chronic alcohol abuse, hepatitis B, or hepatitis C infection.

Within the liver cells, disruption of the urea cycle can also occur in any one of its five steps. Ornithine transcarbamylase deficiency (OTCD) is an inherited metabolic disorder that results in a full or partial enzyme deficiency in step 2, affecting the production of citrulline from ornithine and carbamoyl phosphate.

Hyperammonemia in adults, resulting from cirrhosis or late-onset metabolic disorders, can result in deficits in attention and other cognitive impairments. They are also at higher risk of death from liver failure. In neonates with early-onset enzyme deficiency, developmental delays can be expected. If not diagnosed and treated, these infants risk coma and death. How elevated ammonia damages the brain to produce cognitive and developmental delays is not yet fully understood; however, disturbances in amino acid and neurotransmitter levels, disruptions in ion channel function, and energy deficits in the brain have been proposed as possible mechanisms.

The urea cycle describes how liver cells convert ammonia to urea. Ammonia is a toxic waste product of protein catabolism. Land animals must convert ...

Education

JoVE Core

Biology

Human Biology

Osmoregulation and Excretion

KEY TERMS AND CONCEPTS

liver detox and the urea cycle

The urea cycle is a liver pathway that converts ammonia into urea. Ammonia is a toxic waste product made during protein catabolism. Land animals must change ammonia into the less toxic urea so the kidneys can remove it in urine. Marine animals can excrete ammonia directly because water dilutes it to safer levels.

The cycle has five main steps. First, ammonia is converted to carbamoyl phosphate. Next, ornithine is added as carbamoyl phosphate becomes citrulline. Citrulline then forms argininosuccinate with aspartate and ATP, which provides chemical energy.

In the later steps, argininosuccinate becomes arginine and fumarate is released as a by-product. Then arginine is used to form urea and ornithine. Ornithine is used again in the second step and regenerated in the last step, so it keeps recycling through the pathway. For this reason, the urea cycle is also called the ornithine cycle.

If the cycle is interrupted, blood ammonia can rise, which is called hyperammonemia. This can happen at the organ level if scar tissue blocks blood flow to the liver. Scar tissue, or cirrhosis, can result from chronic alcohol abuse, hepatitis B, or hepatitis C infection. Disruption can also happen inside liver cells at any one of the five steps.

One inherited metabolic disorder is ornithine transcarbamylase deficiency, or OTCD. In OTCD, there is a full or partial enzyme deficiency in step 2, which affects the production of citrulline from ornithine and carbamoyl phosphate. Hyperammonemia in adults, such as from cirrhosis or late-onset metabolic disorders, can lead to attention problems and other cognitive impairments. These adults are also at higher risk of death from liver failure. In neonates with early-onset enzyme deficiency, developmental delays can be expected, and untreated infants may develop coma and die. The exact way elevated ammonia damages the brain is not fully known, but changes in amino acids and neurotransmitters, ion channel disruption, and brain energy deficits have been suggested.

Liver Detox and the Urea Cycle

kidney structure

How Kidneys Filter Blood and Make Urine

The kidneys are two bean-shaped organs in the upper abdomen that filter blood and help keep water and electrolytes in balance. They receive blood from the heart through the renal arteries, and they send filtered blood away through the renal veins. The renal arteries enter the kidney at the hilum, the concave inner surface of the bean shape. From there, they branch into smaller vessels and capillaries. This branching helps move blood through the kidney for filtering. The thick outer layer of...

filtration and urine formation

Kidney Nephrons and Urine Control

Kidney nephrons and urine control depend on filtration, reabsorption, secretion, and excretion. The kidneys filter nearly 180 liters of blood each day. They first remove water and dissolved substances, then return nearly all of the filtrate to the bloodstream with help from osmoregulatory hormones. This process clears wastes and toxins while keeping water and electrolyte levels balanced. Most of these jobs happen in the tiny nephrons inside the kidneys. Blood enters the nephron’s renal...

The urea cycle is a liver pathway that converts ammonia into urea. Ammonia is a toxic waste product made during protein catabolism. Land animals must change ammonia into the less toxic urea so the kidneys can remove it in urine. Marine animals can excrete ammonia directly because water dilutes it to safer levels. The cycle has five main steps. First, ammonia is converted to carbamoyl phosphate. Next, ornithine is added as carbamoyl phosphate becomes citrulline. Citrulline then forms...

hormonal regulation

Renin-Angiotensin Control of Blood Pressure

Renin-angiotensin control of blood pressure is a hormone system that helps the kidneys manage water and electrolytes. It also supports osmoregulation, which is the body’s control of water and salt balance. The system begins in the kidneys near the renal corpuscle, where juxtaglomerular cells sit beside the afferent and efferent blood vessels. As nephrons filter blood, these cells monitor blood pressure. If pressure drops, they release renin into the bloodstream. Renin acts on angiotensinogen,...

osmoregulation in fishes

Fish Water and Salt Balance

Fish water and salt balance helps keep their cells from swelling or shrinking in changing environments. Cells in a hypotonic, or low-salt, fluid can swell and burst. Cells in a hypertonic fluid, which has a higher salt concentration, can shrivel and die. Fish use osmoregulation to control water and dissolved ions such as sodium and chloride. Osmosis is the movement of water across a membrane that lets water pass. Water moves in both directions, but the net flow goes toward the side with more...

osmoregulation in insects

Malpighian Tubules and Water Saving

Malpighian tubules help insects remove waste and conserve water. These specialized structures are found in the digestive systems of many arthropods, including most insects. They are usually arranged in pairs, and their twisted shape gives them more surface area. The tubules extend from the digestive tract, usually between the midgut and hindgut, into the hemolymph. Hemolymph is the fluid that mixes blood and interstitial fluid in insects and other arthropods, and in most mollusks. Unlike many...

comparative excretory systems

Nitrogen Waste in Animal Excretion

Animals use different excretory strategies to remove waste from the body. These strategies matter because most waste must be dissolved in water before it can leave the body. That means excretion is closely tied to water balance. Nitrogenous wastes are some of the most important animal wastes. Nitrogen is released when proteins and nucleic acids are broken down for energy or turned into carbohydrates and fats. Proteins become amino acids, and nucleic acids become nitrogenous bases. The...

what are osmoregulation and excretion?

Water Balance and Waste Removal in Animals

Water balance and waste removal in animals help keep body fluids stable. Organisms must maintain a constant temperature and pH, along with specific solute levels, to support life functions. Osmoregulation is the process that keeps water and solute levels in balance. Osmosis is the movement of water from solutions with lower ion concentrations, or lower osmolarities, to solutions with higher ion concentrations. It happens because two solutions are separated by a semipermeable membrane. Bodily...

key terms and concepts

Learn how the liver turns toxic ammonia into urea, why ornithine recycles through the cycle, and what happens when hyperammonemia disrupts this pathway.

Liver Detox and the Urea Cycle | JoVE K12

JoVE Core series brings biology to life through over 300 concise and easy-to-understand animated video lessons that explain key concepts in biology, plus more than 150 scientist-in-action videos that show actual research experiments conducted in today’s laboratories.

biology

myJoVE Corporation

structural-organization-of-the-human-body-an-overview

Structural Organization of the Human Body: An Overview

It is convenient to consider the body&#39;s structures in terms of fundamental levels of organization that increase in complexity: subatomic particles, ...

Tissues

Tissues are a group of cells that share a common embryonic origin. Microscopic observation reveals that the cells in a tissue share morphological features ...

Cells with similar structure and function are grouped into tissues. A group of tissues with a specialized function is called an organ. There are four main ...

Mitochondria

The Endoplasmic Reticulum

Introduction to Cytoskeleton

What are Membranes?

1. Obtain, evaluate, and communicate information to explain how differences in cellular structure (mitochondria, cytoskeletal structure, endoplasmic reticulum, cell membrane) lead to differences in the function and organization of the four tissue types (epithelial, connective, muscular, and nervous).

9-12.HA.1.1

Introduction to the Integumentary System

The integumentary system is the organ system that comprises the skin and its associated structures. It is the largest system in the human body and plays a ...

Cells of the Epidermis

The epidermis is made of four or five layers of epithelial cells, depending on its location in the body. From deep to superficial, these layers are the ...

Papillary Dermis

Dermis
The dermis might be considered the &#34;core&#34; of the integumentary system, as distinct from the epidermis and hypodermis. It contains blood and ...

Layers of the Epidermis

The epidermis, the outermost layer of the skin, is composed of several distinct layers. From deep to superficial, the layers of the epidermis are as ...

accessory-structures-of-the-skin-sweat-glands

Accessory Structures of the Skin: Sweat Glands

Sweat glands or sudoriferous glands are one of the important accessory structures of the skin. They are small, coiled tubular structures located in the ...

accessory-structures-of-the-skin-hair-and-hair-follicles

Accessory Structures of the Skin: Hair and Hair Follicles

Hair and hair follicles are integral components of the integumentary system. Hair is a filamentous structure composed mainly of a protein called keratin. ...

Accessory Structures of the Skin: Nails

Nails are one of the important accessory structures of the skin. They are hard, protective structures that cover the dorsal surface of the distal ...

2. Obtain, evaluate, and communicate information to describe how the structures of the integumentary system and its accessory organs contribute to its function. Examples: how the layers of the skin contribute to homeostasis, the role of glands in thermoregulation and in hydration of skin and mucous membranes, the protective functions of hair and nails

9-12.HA.1.2

Thermoregulation

The body regulates core temperature through negative feedback mechanisms.
When the core temperature drops, thermoreceptors send signals to the ...

Defense Mechanism Against Infection

Natural flora, body system defenses, and inflammation are natural barriers of the body against infectious agents regardless of previous exposure. Normal ...

Surface Membrane Barriers

Surface barriers such as the skin and mucous membranes are the body&#39;s initial defense against pathogens, offering physical and chemical protection.
...

a. Construct an explanation of the relationships between the integumentary system and other organ systems, including the body's mechanisms for maintaining homeostasis. Examples: Explain how changes in vessel diameter and evaporation of water over the skin contribute to thermoregulation (cardiovascular). Explain how sweat is used to excrete nitrogenous waste from the blood (cardiovascular). Explain how the skin and mucous membranes create a barrier against infection (immune system).

9-12.HA.1.2.a

Introduction to the Skeletal System

The skeletal system is the central framework of the body, consisting of different connective tissues: bones, cartilage, tendons, and ligaments.
Components ...

Classification of Bones

The bones of the human skeletal system are of varied shapes, sizes, and functions. They can be classified based on their shape and function into four ...

Overview of the Axial Skeleton

The skeleton is subdivided into two major divisions&#8212;the axial skeleton and the appendicular skeleton. The axial skeleton forms the vertical, central ...

Introduction to Joints

The adult human body usually has 206 bones, and except for the hyoid bone in the neck, each bone is connected to at least one other bone. Joints are the ...

Joints

Joints, also called articulations or articular surfaces, are points at which ligaments or other tissues connect adjacent bones. Joints permit movement and ...

3. Develop and use a model to illustrate how the structures of the skeletal system contribute to its function. Examples: Create a diagram or 3D model to illustrate bone shape, joint types, and bones in the appendicular and axial skeletons. Use models to illustrate the role of the skeletal system in movements around joints, support of a body structure, and protection of soft tissues.

9-12.HA.1.3

bone-formation-by-endochondral-ossification

Bone Formation by Endochondral Ossification

Bone formation, or ossification, begins around the sixth to seventh week of embryonic development. Most bones develop from a cartilaginous template ...

bone-formation-by-intramembranous-ossification

Bone Formation by Intramembranous Ossification

Intramembranous ossification is one of the two processes involved in the development of bones within an embryo. The flat bones of the face, most of the ...

Bone Remodeling and Repair

a. Obtain, evaluate, and communicate information describing the growth and development of the skeletal system.

9-12.HA.1.3.a

The Functions of the Skeletal System

The most apparent functions of the skeletal system are support, protection, and movement. However, bone tissue also performs several other critical ...

Skeleton and Calcium Homeostasis

Calcium is not only the most abundant mineral in bone but also the most abundant mineral in the human body. Calcium ions are needed for bone ...

The Bone Matrix

Bone contains a relatively small number of cells entrenched in a matrix of collagen fibers that provide an adherent surface for inorganic salt ...

Overview of Hematopoiesis

Hematopoiesis, or hemopoiesis, is the production of the formed elements in blood from common progenitors, called hematopoietic stem cells, or HSCs.
During ...

b. Construct an explanation of the relationships between the skeletal system and other organ systems, including the body's mechanisms for maintaining homeostasis. Examples: Explain the role of spongy bone in hematopoiesis (cardiovascular system) and leukopoiesis (immune system). Explain how the storage of minerals in bone contributes to homeostasis.

9-12.HA.1.3.b

The Muscular System

The muscular system includes the skeletal, smooth, and cardiac muscles that coordinate with each other to carry out functions like movement, digestion, ...

Naming Skeletal Muscles

Skeletal muscle names are based on various factors, such as location, physical traits, and functions.
Often, muscle names indicate their location. For ...

Muscle Coordination and Action

The skeletal muscles can coordinate, oppose, or assist each other to facilitate voluntary body movements.
Depending on their function, a muscle or group ...

Fascicle Arrangement in Skeletal Muscles

Fascicles are bundles of muscle fibers in a skeletal muscle. Muscle fascicle arrangement is directly associated with the power and range of motion of ...

4. Develop and build a three-dimensional model to illustrate the structures of the muscular system, including muscle locations, origins, and insertions, and explain their roles in movement and support. Example: Design and build a model of a lever to illustrate the relationship between bones and muscles and explain their roles in body movement and support.

9-12.HA.1.4

Microscopic Anatomy of Skeletal Muscles

Each skeletal muscle is composed of multiple bundles of elongated multinucleated muscle cells or muscle fibers.
These cells are enclosed by a plasma ...

The Sarcomere

A sarcomere is mainly made up of two types of filaments&#8212; thin filaments containing actin, troponin, and tropomyosin and thick filaments containing ...

excitation-contraction-coupling-in-skeletal-muscles

Excitation-Contraction Coupling in Skeletal Muscles

Excitation-contraction coupling is a series of events that occur between generating an action potential and initiating a muscle contraction. It occurs at ...

Relaxation of Skeletal Muscles

The period of muscle contraction primarily influences the duration of stimulation at the neuromuscular junction (NMJ), the presence of free calcium ions ...

a. Model the cellular physiology of skeletal muscle, including how the cell functions in muscle contraction and relaxation. Example: Use straws and paper to create a model of a sarcomere to illustrate how the fibers move during contraction and relaxation.

9-12.HA.1.4.a

Muscle Recovery and Fatigue

Any intense physical activity escalates the ATP demand in the muscles.
As contractions become vigorous, the compressed blood vessels impair the ...

Muscle Stimulation Frequency

Depending on the demand, motor neurons control the strength of a muscle&#39;s contraction by altering the frequency of action potentials delivered to the ...

b. Obtain, evaluate, and communicate information to explain muscle fatigue and tone in terms of muscle cell physiology.

9-12.HA.1.4.b

Organization of the Nervous System

The nervous system is the primary control and communication center of the body.
The nervous system can be divided into two major categories&#8212;the ...

functional-divisions-of-the-nervous-system

Functional Divisions of the Nervous System

The nervous system senses, integrates, and responds to various stimuli. Based on bodily control, the central nervous system cannot be divided ...

Anatomy of the Brain: Major Regions

The human brain is a complex organ consisting of four main parts &#8212; the cerebrum, the cerebellum, the diencephalon, and the brainstem.
The cerebrum ...

peripheral-nervous-system-ganglia-and-nerves

Peripheral Nervous System: Ganglia and Nerves

The peripheral nervous system consists of nerves, ganglia, and sensory receptors.
Each nerve has an outermost connective tissue layer called the ...

5. Obtain, evaluate, and communicate information explaining the relationship between the structures and functions of the central nervous system and the peripheral nervous system.

9-12.HA.1.5

Action Potential

Neurons communicate by firing action potentials&#8212;the electrochemical signal that is propagated along the axon. The signal results in the release of ...

Propagation of Action Potentials

The Propagation of an action potential is the process by which a nerve impulse is transmitted along the axon. It is a self-propagating process; once ...

Action Potential: Phases of Stimulation

The action potential is a complex electrical event that occurs in excitable cells, such as neurons and muscle cells. It consists of several distinct ...

Voltage-gated Ion Channels

a. Use a model to illustrate the role of action potentials in neural transmission. Clarification: Discussions of sodium-potassium pumps and ion channels are not required.

9-12.HA.1.5.a

Somatic Spinal Reflexes

Somatic spinal reflexes are rapid, involuntary muscular responses to external stimuli that involve the somatic musculature and the spinal cord.
One of the ...

Reflex Activity

A reflex is a quick and automatic response to a stimulus, like pulling your hand away from heat or lifting your foot off a sharp object.&#160;&#160;
A ...

Introduction to Special Senses

Humans have five special senses&#8212;vision, smell, taste, hearing, and equilibrium. All these senses have anatomically distinct receptors to detect ...

b. Construct an explanation of the role of reflex arcs, the central nervous system, and special senses in the response to stimuli to maintain homeostasis and guide behavior. Example: smelling a strong odor initiating a sneeze response using a reflex arc; pupil diameter changing in relation to the amount of light entering the eye Clarification: Discussion of the anatomy and physiology of the sensory organs is not required.

9-12.HA.1.5.b

Neurotransmitters

Neurotransmitters play a crucial role in the communication between neurons in the autonomic nervous system. Neurons in the autonomic nervous system can be ...

Chemical Synapses

Chemical synapses are specialized sites between two neurons or between a neuron and a non-neuronal cell like a muscle, glandular or sensory cell.
Because ...

The Synapse

Neurons communicate with one another by passing on their electrical signals to other neurons. A synapse is the location where two neurons meet to exchange ...

c. Construct an explanation of the role of neurotransmitters in the functions and behavior of the nervous system. Clarification: Discussion of classes of neurotransmitters is not required.

9-12.HA.1.5.c

Functional Brain Systems: Limbic System

The limbic system is a functional brain region consisting of specific parts of the diencephalon and cerebrum.
The limbic lobe of the cerebral cortex ...

functional-brain-systems-reticular-formation

Functional Brain Systems: Reticular Formation

The reticular formation is a complex network of gray and white matter spread across the core of the brainstem.
It is roughly divided into three paired ...

higher-mental-functions-of-brain-learning-and-memory

Higher Mental Functions of Brain: Learning and Memory

Memory is one of the most vital higher mental functions of the brain. Memory is closely related to learning because it enables us to retain information ...

higher-mental-functions-of-the-brain-language

Higher Mental Functions of the Brain: Language

Language is a system of communication that allows the expression of thoughts, ideas, and feelings. The brain processes language in both hemispheres.
...

Motor and Sensory Areas of the Cortex

The cerebral cortex has three functional areas &#8212; the motor, sensory, and association areas.
The motor areas, located in the frontal lobe, control ...

Association Areas of the Cortex

Association areas are regions of the cerebral cortex that do not have a specific sensory or motor function. Instead, they integrate and interpret ...

d. Obtain, evaluate, and summarize scientific findings regarding the biological origin of emotions and memories in distinct regions of the brain. Examples: the role of the frontal lobe in emotional regulation, the regulation of fear response by the amygdala

9-12.HA.1.5.d

Hypothalamic-Pituitary Axis

The response to stress&mdash;be it physical or psychological, acute or chronic&mdash;involves activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis. ...

6. Construct an explanation of how the interdependence of the nervous and endocrine systems maintains homeostasis.

9-12.HA.1.6

Liver Detox and the Urea Cycle

Description

Transcript

Tags

More videos by Standards